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A model based methodology for knock prediction in SI engines
Control Control 9th IFAC France, International Orléans, June Symposium 23-27, 2019 on Advances in Automotive Orléans, France, June 23-27, 2019 Control Available online at www.sciencedirect.com Orléans, June Symposium 23-27, 2019 on Advances in Automotive 9th IFAC France, International Control Orléans, France, June 23-27, 2019
ScienceDirect A model based methodology for knock prediction in SI engines A model based methodology for knock IFAC PapersOnLine 52-5 (2019) 291–296prediction A model based methodology for knock prediction in in SI SI engines engines A model based methodology for knock prediction in SI engines B. Rossomando*, C. Fruncillo*, I. Arsie*, M. Comentale*, M. De Cesare** A model based methodology knock predictionM.inDeSI engines B. Rossomando*, C. Fruncillo*,for I. Arsie*, M. Comentale*, Cesare**
B. Rossomando*, C. Fruncillo*, I. Arsie*, M. Comentale*, M. De Cesare** B. Rossomando*, C. Fruncillo*, I. Arsie*, M. Comentale*, M. De Cesare** *Dept. of Industrial Engineering, University of Salerno Fisciano Italy; Engineering, (e-mail: brossomando@ B. Rossomando*, C. Fruncillo*, I. Arsie*, M. Comentale*, M. De Cesare** *Dept. of (SA) Industrial University ofunisa.it). Salerno *Dept. of Industrial Engineering, University of(e-mail: Salerno **Magneti Marelli Powertrain, Bologna Italy Fisciano (SA) Italy; (e-mail: brossomando@ unisa.it). *Dept. of Industrial University ofunisa.it). Salerno Fisciano (SA) Italy; Engineering, (e-mail: brossomando@ [email protected]) **Magneti Marelli Bologna Italyunisa.it). (e-mail: Fisciano (SA) Italy;Powertrain, (e-mail: brossomando@ **Magneti Marelli Powertrain, Bologna Italy (e-mail: [email protected]) *Dept. of Industrial Engineering,Bologna University of(e-mail: Salerno **Magneti Marelli Powertrain, Italy [email protected]) Fisciano (SA) Italy; (e-mail: brossomando@ unisa.it). [email protected]) Marelli Powertrain, Bologna (e-mail: Abstract: In spark-ignition**Magneti engines, knock control represents one ofItaly the most critical issue to reach optimal [email protected]) thermal efficiency. The paper deals with the development of a methodology aimed at evaluating most Abstract: In spark-ignition engines, knock control represents one of the most critical issue to reachthe optimal Abstract: In spark-ignition engines, knock control represents one of the most critical issue to and reachknocking optimal suited spark advance to achieve the right compromise between performance optimization thermal The paper deals knock with the development of one a methodology aimed at evaluating the most Abstract:efficiency. In(KLSA). spark-ignition engines, control represents of the most critical issue to reach optimal thermal efficiency. The paper deals withisthe development of a methodology aimed at evaluating the most occurrence The methodology based on combustion simulation via a two-zone 0D knocking model in suited spark advance to achieve the right compromise between performance optimization and thermal efficiency. The paper deals with the development of a methodology aimed at evaluating the most suited spark advance to achieve the right compromise between performance optimization and knocking which the cycle-by-cycle variation (CCV) is described by a model parameter that impacts on the turbulence occurrence (KLSA). The methodology is based on combustion simulation via a two-zone 0D model in Abstract: In(KLSA). spark-ignition engines, knock represents one of the most critical issue to and reach optimal suitedatspark advance to achieve the right compromise between performance occurrence The methodology is control basedofon combustion simulation viaoptimization a two-zone 0D knocking model in level inlet valve closing. The auto-ignition the unburnt mixture is described by a thermodynamic which the cycle-by-cycle variation (CCV) is described by a model parameter that impacts on the turbulence thermal efficiency. The paper deals(CCV) withisthe development of a methodology aimed at evaluating the most occurrence (KLSA). The methodology on combustion simulation via a two-zone 0D model in which the cycle-by-cycle variation isbased described by aevaluated model parameter that impacts on the turbulence equation derived from literature while knock intensity is by a stochastic approach. The method level atthe inlet valve closing. The the auto-ignition of the by unburnt mixture is described by aonthermodynamic suited spark advance to achieve right compromise between performance optimization and knocking which cycle-by-cycle variation (CCV) is described a model parameter that impacts the turbulence level at evaluating inlet valvethe closing. The auto-ignition ofcycles, the unburnt mixture described by a thermodynamic allows percentage of knocking on ais the spark actuated. The equation derived from literature while knock intensity isdepending evaluated by stochastic approach. Themodel method occurrence (KLSA). The methodology is based combustion simulation via a advance two-zone 0D in level at inlet valve closing. The auto-ignition ofon the unburnt mixture described by aonthermodynamic equation derived from literature while knock intensity iscollected evaluated by aisstochastic approach. The method validation has been carried out vs. experimental data at the engine test rig a 4 cylinders allows evaluating the percentage of knocking cycles, depending on the spark advance actuated. The which the cycle-by-cycle variation (CCV) is described by a model parameter that impacts on the turbulence equation derived from while knock intensity evaluated by athe stochastic approach.actuated. The method allows evaluating the literature percentage of knocking cycles, depending on spark advance The turbocharged byThe comparing predicted and is experimental MAPO. validation hasGDI beenengine, carried out vs. data collected at on the engine rig aonthermodynamic a 4 cylinders level at evaluating inlet closing. auto-ignition the mixture described by allows percentage ofexperimental knockingofcycles, depending the sparktest advance The validation hasvalve beenthe carried out vs. experimental dataunburnt collected at theis engine test rig on actuated. a 4 cylinders turbocharged engine, byFederation comparing and experimental MAPO. Keywords: SI GDI Engine; Combustion Knock Detection; Model-based Calibration andaDiagnostics equation derived from literature while knock intensity is evaluated aElsevier stochastic The method © 2019, IFAC (International of predicted Automatic Control) Hosting by Ltd. All validation has been carried vs.Control; experimental data collected atby the engine testapproach. rig rights on 4reserved. cylinders turbocharged GDI engine, byout comparing predicted and experimental MAPO. allows evaluating the Combustion percentage of knocking cycles, depending on the spark advance The Keywords: SI GDI Engine; Control; Knock Detection; Model-based Calibration andactuated. Diagnostics turbocharged engine, by comparing predicted experimental MAPO. and Keywords: SI Engine; Combustion Knock Detection; Model-based Calibration andaDiagnostics validation has been carried out vs.Control; experimental data collected at the engine test rig on 4 cylinders anomalous combustionCalibration may occurand dueDiagnostics to self-ignition of the Keywords: SI GDI Engine; Combustion Control; Knock Detection; Model-based and turbocharged engine, by comparing predicted experimental MAPO. 1. INTRODUCTION mixture, thus resulting in knocking. anomalous combustion may occur due to self-ignition of the anomalous combustion may occur dueDiagnostics to self-ignition of the 1.SI INTRODUCTION Engine; Combustion Control; Knock Model-based Calibration and The knock represents most critical issue to improve engine In the last Keywords: twenty years the energy question and its impact on Detection; mixture, thus resultingthe inmay knocking. 1. INTRODUCTION anomalous combustion occur due to self-ignition offrom the mixture, thus resulting in knocking. fuel economy and prevents the combustion controlengine the has assumed global importance. 1. INTRODUCTION The knock represents the most critical issue to improve In theenvironment last twenty years the energy question and its impactThe on mixture, thus resulting in knocking. The knock represents the most critical issue to improve engine In the last twenty years the energy question and its impact on achieving the best efficiency, constraints on requirement to reduce greenhouse gasesimportance. has led most fuel economy andthermal prevents the combustion control offrom the environment has the assumed global anomalous combustion may dueimposing to self-ignition the The knock represents the mostoccur critical issue to improve In theenvironment last twenty years energy question and its impactThe on fuel economy and Inprevents the combustion controlengine from the has assumed global importance. The 1. INTRODUCTION the spark advance. order to reduce the occurrence of the governments to set ambitious targets for the improvement of achieving the best thermal efficiency, imposing constraints on requirement to reduce greenhouse gasesimportance. has led most mixture, thus in knocking. fuel economy andthermal prevents the combustion controlandfrom the environment has assumed global The achieving the resulting best efficiency, imposing constraints on requirement to reduce greenhouse gases has led most knocking phenomenon, the enrichment of the mixture the fuel economy (Reitz 2013; Wang et al. 2013). the spark advance. In order to reduce the occurrence of the governments to set ambitious targets for the improvement of The knockthe represents most issue improve engine In the last twenty years thegreenhouse energy question its impact on achieving best angle thermal efficiency, imposing constraints on requirement to non-ideal reduce gases has ledleads most spark advance. Inthe order tocritical reduce the to occurrence of the governments to set ambitious targets for theand improvement of delay of the spark advance arecombustion generally adopted (Leduc In addition, the combustion in the engines to the knocking phenomenon, the enrichment of the mixture and the fuel economy (Reitz 2013; Wang et al. 2013). fuel economy and prevents the control from the environment has assumed global importance. The the spark advance. In order to reduce the occurrence of the governments to set ambitious targets for the improvement of knocking phenomenon, the enrichment of the mixture and fuel economy (Reitz 2013; Wang et al. 2013). et al. 2003; Hettinger et al. 2009), which results in a drastic the production ofnon-ideal other species such as nitrogen oxides, carbon delay of the spark angle advance are generally adopted (Leduc In addition, the combustion in the engines to achieving thespark best angle thermal efficiency, imposing constraints on requirement to reduce gases has ledleads most knocking phenomenon, the enrichment of the mixture and the fuel economy (Reitz 2013;greenhouse Wang and et al.solid 2013). of the advance areunder generally adopted (Leduc In addition, the non-ideal combustion in the engines leads to delay decrease of Hettinger thermal efficiency high load engine monoxide, unburnt hydrocarbons particulates, which et al. 2003; et al. 2009), which results in a drastic the production of other species such as nitrogen oxides, carbon the spark advance. In order to reduce the occurrence of the governments to set ambitious targets for the improvement of delay the spark angleetadvance are which generally adopted In theofnon-ideal combustion in the engines to et al. of 2003; Hettinger al. 2009), results in a (Leduc drastic theaddition, production other species such ashealth. nitrogen oxides,leads carbon conditions. are harmful and dangerous to human decrease of Hettinger thermal etefficiency under high load engine monoxide, unburnt hydrocarbons and particulates, which operating knocking phenomenon, the enrichment of the mixture and the fuel economy (Reitz 2013; Wang et as al.solid 2013). et al. 2003; al. 2009), which results in a drastic the production of other species such nitrogen oxides, carbon decrease of thermal efficiency under high load engine monoxide, unburnt hydrocarbons and solid particulates, which During the development of anareengine, oneadopted of the(Leduc main The goal of research in the automotive field is therefore to limit operating conditions. are harmful and dangerous to human health. delay of the spark angle advance generally In addition, the non-ideal combustion in the engines leads to decrease ofis thermal efficiency under value high of load engine monoxide, unburnt hydrocarbons and health. solid particulates, which conditions. are much harmfulas and dangerous to human objectives to define theof2009), maximum spark as possible theautomotive emissions of pollutants the operating During the development an engine, one ofinthe the main The goal of research in the field is therefore to limit et al. 2003; Hettinger et al. which results a drastic the production ofdangerous other species such ashealth. nitrogen oxides,into carbon operating conditions. are harmful and to human During the development of an engine, one of the main The goal of research in the automotive field is therefore to limit advance to be adopted, in order to maximize thermal efficiency atmosphere, ensuring reduced consumption and at the same objectives is to define the maximum value of the spark as much as possible the emissions of pollutants into the decrease of thermal efficiency under high load engine monoxide, unburnt hydrocarbons and solid particulates, which During theisdevelopment an engine,value one of of the spark main The goal ofasresearch in the field is therefore to limit to define theof maximum the as much possible theautomotive emissions of pollutants into the while preventing intensive knocking. The experimental time maximum performance. The increase of efficiency in objectives advance toconditions. be adopted, in order to maximize thermal efficiency atmosphere, ensuring reduced consumption and at the same operating are harmful and dangerous to human health. objectives is to define the maximum value of the spark as much as possible the emissions of pollutants into the advance to be adopted, in order to maximize thermal efficiency atmosphere, ensuring reduced consumption and at the same identification of this intensive variable, indicated as KLSA (Knockinternal combustion engines, to The meetincrease the increasingly stringent preventing knocking. The experimental time maximum performance. of efficiency in while During the of also an engine, The one of the main The of research in reduced the automotive field is therefore limit advance to bedevelopment adopted, inisorder to maximize thermal efficiency atmosphere, ensuring consumption and at guideline thetosame preventing intensive knocking. experimental timegoal maximum performance. The increase of the efficiency in while limited spark advance), accomplished by an expensive and anti-pollution regulations, has therefore become identification of this variable, also indicated as KLSA (Knockinternal combustion engines, to meet the increasingly stringent objectives is to define the maximum value of the spark as much as possible the emissions of pollutants into the while preventing intensive knocking. The experimental time maximum performance. The increase of efficiency in of this variable, also indicated asmeasurement KLSA (Knockinternal combustion engines, to meet the increasingly stringent identification time consuming process that involves the of to follow. limited spark advance), isorder accomplished by as anKLSA expensive and anti-pollution regulations, has therefore become the guideline advance to be of adopted, inis to maximize efficiency atmosphere, ensuring reduced consumption andthe at guideline the same limited identification thiscycles, variable, also indicated (Knockinternal combustion engines, meet the become increasingly stringent spark advance), accomplished by thermal an expensive and anti-pollution regulations, hastotherefore numerous pressure due to the strong variability of the In the Spark Ignition (SI) engines, various constructive time consuming process that involves the measurement of to follow. while preventing intensive knocking. experimental time maximum performance. The increase of the efficiency in time limited spark advance), isand accomplished byThe an expensive and anti-pollution has therefore become guideline consuming process that involves the measurement of to follow. knocking phenomenon the cycle-by-cycle variation solutions haveregulations, beenengines, developed. The up-to-date technology numerous pressure cycles, due to the strong variability of the In the Spark Ignition (SI) engines, various constructive identification of this variable, also indicated as KLSA (Knockinternal combustion to meet the increasingly stringent time consuming process that the to measurement of to follow. pressure cycles,engines. due involves to the strong variability of this the In the the Spark Ignition (SI) engines, various constructive (CCV) of spark ignition Incycle-by-cycle order overcome where direct in The the up-to-date combustion chamber numerous knocking phenomenon and the variation solutions have beeninjection developed. technology limited spark advance), isand accomplished by an expensive and anti-pollution regulations, has therefore become the guideline numerous pressure cycles, due to the strong variability of the In the Spark Ignition (SI) engines, various constructive knocking phenomenon the cycle-by-cycle variation solutions have been developed. The up-to-date technology issue, model based methods developed to providethis an combined ainjection turbo-compression system, chamber proves (CCV) of spark ignition engines. In order tomeasurement overcome where the with direct in the up-to-date combustion time consuming process that are involves the to of to follow. knocking phenomenon and the In cycle-by-cycle variation solutions beeninjection developed. technology (CCV) of spark ignition engines. order overcome this where thehave direct in The the combustion chamber evaluation of the phenomenon with the minimum cost in terms particularly effective especially when the displacement is issue, model based methods are developed to provide an combined with a turbo-compression system, proves numerous pressure cycles, due to the strong variability of the In the Spark Ignition (SI) engines, various constructive (CCV) of spark ignition engines. In order to to overcome where the direct ainjection in followed the combustion chamber issue, model based methods are developed providethis an combined with turbo-compression system, proves of experimental resources. Thewith aim of this work iscost therefore to reduced: the reduction of the path the flame front, of the phenomenon the minimum in terms particularly effective especially whenup-to-date thebysystem, displacement is evaluation knocking phenomenon and the the cycle-by-cycle variation solutions have beena developed. The technology issue, model based methods are developed to provide an combined with turbo-compression proves evaluation of the phenomenon with minimum cost in terms particularly effective especially when the displacement is provide a methodology for predicting the incipient knock the increase of turbulence in the chamber, the best thermal of experimental resources. The aim of this work is therefore to reduced: the reduction of the path followed by the flame front, (CCV) of spark ignition engines. In order to overcome this where the direct injection in followed the combustion chamber evaluation ofbased theresources. phenomenon minimum inmodel terms particularly effective especially when thebytemperature displacement is of experimental Thewith aim the of this work iscost therefore to reduced: the reduction the path the flame front, conditions, on methods a phenomenological combustion efficiency achieved byof reducing the charge and provide a methodology for predicting the incipient knock the increase of turbulence in the chamber, the best thermal issue, model based are developed to provide an combined with a turbo-compression system, proves of experimental resources. The aim of thisthe work is therefore to reduced: reduction of theinmake path bythe thebest flame front, provide a methodology for predicting incipient knock the increase of turbulence the followed chamber, thermal which takes into account the cycle-by-cycle variation (CCV). the heat the exchange surface, these engines particularly conditions, based on a phenomenological combustion model efficiency achieved byespecially reducing the charge temperature and evaluation of the phenomenon with the minimum cost in terms particularly effective when the displacement is conditions, provide a methodology for predicting the incipient knock the increase of turbulence in the chamber, the best thermal based on a phenomenological combustion model efficiency achieved by reducing the charge temperature and The methodology presentsthe reduced and efficient performing. Themake downsizing allows a reduction which takesbased intoresources. account cycle-by-cycle variation (CCV). the heat and exchange surface, these engines particularly of experimental The aimcomputational of this work isdemand therefore to reduced: the reduction ofreducing the path followed bytemperature the flame front, conditions, on a advance phenomenological combustion model efficiency achieved byconsumption the charge and which cycle-by-cycle variation (CCV). takes into account the the heatspecific exchange surface, make these engines particularly allows setting the spark which guarantee high thermal of the fuel (BSFC) at partial load The methodology presents reduced computational demand and efficient and performing. The downsizing allows a reduction provide a methodology for predicting the incipient knock the increase of turbulence in the chamber, the best thermal which takes into account the cycle-by-cycle variation (CCV). the heat and exchange surface, these (Leduc engines The methodology presents reduced demand and efficient Themake downsizing allowsetparticularly aal. reduction efficiency without theaoccurrence ofcomputational knocking. compared to aperforming. naturally aspirated engine 2003). allows setting the spark advance which guarantee high thermal of the specific fuelbyconsumption (BSFC) at partial load conditions, based on phenomenological combustion model efficiency achieved reducing the chargeallows temperature and allows The methodology presents reduced computational demand and efficient and performing. The downsizing a reduction setting the spark advance which guarantee high thermal of the specific fuel consumption (BSFC) at partial load However, under highsurface, load operating conditions, due to the high efficiency without the occurrence of knocking. compared to a naturally aspirated engine (Leduc etpartial al. 2003). which takes into account the cycle-by-cycle variation (CCV). the heatspecific exchange makeengine these engines particularly allows setting the spark advance which guarantee high thermal of the fuel consumption (BSFC) at load efficiency without the occurrence of knocking. compared to a naturally aspirated (Leduc et al. 2003). pressure and temperature reached inconditions, the combustion However, under high load operating due tochamber, the high efficiency methodology reducedofcomputational efficient The downsizing allows withoutpresents the occurrence knocking. demand and comparedand to aperforming. naturally aspirated engine (Leduc etaal. 2003). However, under high load operating conditions, due toreduction the high The pressure and temperature reached in the combustion chamber, allows setting the spark advance which guarantee high thermal of the specific fuel consumption (BSFC) at partial load However, under high load operating conditions, due to the high pressure and temperature reached in the combustion chamber, 291 Copyright © 2019 IFAC efficiency without the occurrence of knocking. compared to atemperature naturally aspirated (Leduc et al.chamber, 2003). pressure and reached engine in the combustion Copyright 2019 IFAC However,© high load operating conditions, due to the high 291 Copyright ©under 2019 IFAC 291 2405-8963 © 2019, IFAC (International of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. pressure and temperature reached inFederation the combustion chamber, Copyright © 2019 IFAC 291 Peer review under responsibility of International Federation of Automatic Control. 10.1016/j.ifacol.2019.09.047 Copyright © 2019 IFAC 291
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or complete chemical kinetics (Livengood et al. 1955; Vandersickel et al. 2012; Shu et al. 2013).
2. KNOCK DETECTION The occurrence of knocking can be experimentally detected by several methods, among which the most common are those based on the analysis of in-cylinder pressure (Draper 1938), crankcase vibration (Wu 2007; Arjmandi et al. 2008), exhaust gas temperature (Abu-Qudais 1996).
An empirical method is used in the current application, based on the consideration that auto-ignition is not instantaneous but there is a period of "incubation" during which the intermediate oxidation compounds are formed. The time interval between the instant when the mixture reaches pre-set temperature and pressure conditions and the instant when the combustion starts appreciably is called ignition delay 𝜏𝜏.
Some synthetic indices are used to quantify the intensity of knocking and they are related to the in-cylinder pressure signal (MAPO and Kint) or the apparent heat release rate (ROHR and CHR). Among these, MAPO (Maximum Amplitude of Pressure Oscillation) is the most widespread and accepted index, in both academy and industry, (Brecq et al. 2003) and it is often used as a reference when it is necessary to compare the behaviour of different engines in terms of knock. It is defined as the maximum of the absolute value of the filtered in-cylinder pressure signal, evaluated within a time window that includes combustion: 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 = 𝑚𝑚𝑚𝑚𝑚𝑚 |𝑝𝑝𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 |
The ignition delay can be expressed as function of the thermodynamic conditions 𝑝𝑝 and 𝑇𝑇𝑢𝑢 of the unburnt mixture, by means of the following relationship (Kalghatgi et al. 2015): 𝐵𝐵
𝜏𝜏(𝑝𝑝, 𝑇𝑇𝑇𝑇) = 𝐴𝐴 𝑒𝑒 𝑇𝑇𝑢𝑢 𝑝𝑝−𝑛𝑛
(2)
where the constants A, n and B are determined experimentally, according to the characteristics of the fuel. An integral function of auto-ignition delay can thus be calculated by the following equation:
(1)
𝑡𝑡
𝐼𝐼(𝑡𝑡) = ∫0
The calculation of the MAPO is aimed at estimating with sufficient confidence the value of the maximum spark advance that can be adopted without incurring in severe knock (KLSA).
𝑑𝑑𝑑𝑑
𝜏𝜏(𝑝𝑝,𝑇𝑇)
(3)
Considering the whole process, if at the time 𝑡𝑡𝑓𝑓 , in which combustion is completed, the integral is lower than 1, it is possible to assume that knock does not occur (Livengood et al. 1955).
KLSA can be evaluated by a statistical approach (95th percentile) (Leppard 1982; Galloni et al. 2014) or by defining a critical value of MAPO which is an increasing function of the engine speed. In the latter case, for the definition of the KLSA the whole engine operating range has to be explored by varying the spark advance; for each spark advance the percentage of knocking cycles is defined, i.e. those that exceed the established threshold. Starting from this information the spark advance corresponding to the incipient knock is identified (De Bellis et al. 2015).
The index MAPO, relative to the intensity of the knock, has been defined in this work as the sum of two contributions; the former is related to the effect of normal combustion, the second is related to the effect of the proper knock:
𝑀𝑀𝑀𝑀𝑀𝑀𝑂𝑂𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚,𝑠𝑠𝑠𝑠𝑠𝑠 = 𝑘𝑘1 𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑙𝑙𝑙𝑙𝑙𝑙 + 𝑘𝑘2 max(𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 − 1) 𝛥𝛥𝛥𝛥𝐾𝐾𝐾𝐾
(4)
where: - 𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 represents the value of I(t) at the EVO (Exhaust Valve Opening); - 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑙𝑙𝑙𝑙𝑙𝑙 it is the threshold to discriminate a normal combustion from a knocking one, that is defined by the empirical formula 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑙𝑙𝑙𝑙𝑙𝑙 = 𝑟𝑟𝑟𝑟𝑟𝑟/2000. - 𝛥𝛥𝛥𝛥𝐾𝐾𝐾𝐾 represents the pressure gradient caused by knocking. It is estimated assuming that when knock starts occurring, all the unburned fuel in the combustion chamber burns instantaneously; considering a constant volume adiabatic combustion, it is calculated as:
3. KNOCKING MODELING In order to adequately describe the knock phenomenon, in terms of onset and intensity, the first step is to identify a modelling approach that allows representing the processes that influence the knock, i.e. combustion and cycle- by- cycle variation. In this work the combustion process simulation is performed by a two-zone model (Arsie et al., 2004), that was previously validated vs. the engine under study. The CCV is taken into account by the model parameter 𝐶𝐶𝑘𝑘 that describes the level of turbulence at the inlet valve closing (IVC). This parameter allows characterizing the combustion process in terms of combustion speed, maximum pressure 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚 and related angular position 𝜃𝜃𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 .
𝛥𝛥𝛥𝛥𝐾𝐾𝐾𝐾 =
𝑄𝑄KO (𝑘𝑘−1) 𝑉𝑉𝐾𝐾𝐾𝐾
(5)
in which 𝑉𝑉𝐾𝐾𝐾𝐾 is the volume of the combustion chamber when the knock appears (KO: knock onset); k is the ratio between the specific heats of the mixture; 𝑄𝑄KO represents the quantity of chemical energy released when the mixture burns, defined as:
In order to identify the start of knock, it is mandatory to evaluate the ignition delay of the unburnt mixture. There are several models of the ignition delay ranging from simple empirical expressions to complex formulations with reduced
𝑄𝑄KO = (1 − 𝑥𝑥𝑏𝑏,𝐾𝐾𝐾𝐾 ) 𝑚𝑚𝑓𝑓 𝐻𝐻𝑖𝑖 292
(6)
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where 𝑥𝑥𝑏𝑏,𝐾𝐾𝐾𝐾 indicates the burnt fraction at the beginning of the knock; 𝑚𝑚𝑓𝑓 is the amount of fuel in the combustion chamber at the beginning of the cycle; 𝐻𝐻𝑖𝑖 it is the lower heating value of the fuel. - 𝑘𝑘1 and 𝑘𝑘2 are model parameters to be tuned.
kHz is then defined by means of a frequency domain analysis. Once the signal has been filtered, the MAPO is evaluated from the maximum value of the signal module. The pressure cycle without the knocking effect is achieved by applying a low pass filter (low pass LP) with a cut-off frequency of 10 kHz that allows purging the signal from those frequencies related to knocking (Galloni et al. 2014; Brecq et al. 2003).
This approach provides a value of the average MAPO, because, given the uncertainty of the combustion process and knocking phenomenon, more cycles with the same level of 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 can be characterized by different MAPO values.
4.2 Combustion and CCV Model Validation
For this reason, the model is initially tuned considering the mean MAPO values, evaluated experimentally by means of a statistical analysis of the experimental data. In order to describe the randomness of the knocking phenomenon, in addition to the knowledge of the average MAPO, a further relation has to be identified that expresses the standard deviation of the experimental data. This relationship is very similar to (eq. 4) and is dependent on two further parameters 𝑘𝑘3 and 𝑘𝑘4 : 𝑅𝑅𝑅𝑅𝑆𝑆𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀,𝑠𝑠𝑠𝑠𝑠𝑠 = 𝑘𝑘3 𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑙𝑙𝑙𝑙𝑙𝑙 + 𝑘𝑘4 max(𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 − 1) 𝛥𝛥𝛥𝛥𝐾𝐾𝐾𝐾
293
Model validation is accomplished by considering the average pressure cycle for each operating condition. The parameter 𝐶𝐶𝑘𝑘 is identified by a least square minimization of the following error function: 𝑝𝑝𝑠𝑠𝑠𝑠𝑠𝑠,𝜃𝜃 − 𝑝𝑝𝑒𝑒𝑒𝑒𝑒𝑒,𝜃𝜃
𝑓𝑓 = √( ∑𝑁𝑁 𝜃𝜃=1 ( 1 2
1
𝑁𝑁
𝑝𝑝𝑒𝑒𝑒𝑒𝑒𝑒,𝜃𝜃
2
) )+
1 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑠𝑠𝑠𝑠𝑠𝑠 − 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑒𝑒𝑒𝑒𝑒𝑒 2
𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑒𝑒𝑒𝑒𝑒𝑒
(8)
where 𝑝𝑝𝑠𝑠𝑠𝑠𝑚𝑚,𝜃𝜃 and 𝑝𝑝𝑒𝑒𝑒𝑒𝑒𝑒,𝜃𝜃 are the simulated and experimental in-
(7)
cylinder pressure, respectively, while 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑠𝑠𝑠𝑠𝑠𝑠 and 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑒𝑒𝑒𝑒𝑒𝑒 are
4. EXPERIMENTAL ANALYSIS AND VALIDATION
the corresponding maximum values.
The experimental data are measured at the test rig on a production 4 cylinders, 1.4 liters, turbo-charged GDI engine.
Figure 1 shows a comparison between experimental and simulated in-cylinder pressure for three cycles collected in the same engine operating condition (i.e. test case1), corresponding to the average, minimum and maximum cycles of the CCV distribution.
The data refer to three incipient knock conditions at high load operation and engine speed of 2500, 3500 and 4000 rpm (Tab. 1). Table 1. Engine operating conditions investigated. Test case
1
2
3
Speed [rpm]
2500
3500
4000
SOI [BTDC]
275
308
319
ϑSA [BTDC]
13/12.2/11.5
25.3/24.9/24.3
21.7/21.2/ 20.7
The data were collected by continuously imposing a slight variation of the spark advance (𝜃𝜃𝑆𝑆𝑆𝑆 ) in order to identify the one characterized by the best compromise between high thermal efficiency (high 𝜃𝜃𝑆𝑆𝑆𝑆 ) and knock prevention (low 𝜃𝜃𝑆𝑆𝑆𝑆 ).
Fig. 1. Comparison between simulated and experimental pressure cycle at 2500 rpm. 𝜃𝜃𝑆𝑆𝑆𝑆 = 11.55 [𝑑𝑑𝑑𝑑𝑑𝑑 𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵]
Figure 2 shows the 𝐶𝐶𝑘𝑘 parameter distributions obtained experimentally for the test case 1; the figure evidences the different distributions achieved according with the spark advance variation and the relationship between 𝐶𝐶𝑘𝑘 and the peak pressure value. Each 𝐶𝐶𝑘𝑘 distribution is related to the corresponding distribution of 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚 ; therefore, considering that this set of data can be obtained from the average value 𝑃𝑃̅𝑚𝑚𝑚𝑚𝑚𝑚 and the coefficient of variation 𝐶𝐶𝑉𝑉𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 , it is possible to design a
4.1 Signal Filtration The in-cylinder pressure data have to be suitably processed to define the MAPO and the pressure cycle without the effect of knocking, that is needed to validate the model of combustion and knock. To evaluate MAPO, the signal acquired by the transducer is windowed in a range from the TDC (Top Dead Center) to 60 deg ATDC (After Top Dead Center); subsequently it is filtered through a band-pass filter containing the primary knock frequencies. The range of characteristic frequencies of 10-90 293
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polynomial regression to calculate the distribution of 𝐶𝐶𝑘𝑘 as a function of 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚 .
Fig. 4. Identification of MAPO and 𝜃𝜃𝐾𝐾𝐾𝐾,𝑒𝑒𝑒𝑒𝑒𝑒 Fig. 2. 𝐶𝐶𝑘𝑘 distributions as function of 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚
The whole set of data is divided into a series of pressure intervals containing a number of cycles sufficient for the description of the knocking phenomenon. Within each interval the MAPO has been analysed in terms of average value and standard deviation. The analysis allows defining, for each pressure interval, the corresponding MAPO probability density functions (PDF). As it is shown in figure 5, the PDF of MAPO can be described by a log-normal function due to the non-linearity of the kinetic mechanisms that control the auto-ignition (Spelina et al. 2013). The results show that by increasing the level of pressure, mode, average value and median of each single distribution increase, therefore the intensity of the knocking phenomenon is directly related to its randomness.
Figure 3 shows the experimental distributions of 𝑝𝑝𝑚𝑚𝑎𝑎𝑎𝑎 for the three spark advance values actuated in the test case 1.
Fig. 3. Probability density functions of 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚 As expected (De Bellis et al. 2015; Abraham et al. 1992; Przybyla et al. 2016), the figure exhibits an increase of the maximum average pressure (𝑃𝑃̅𝑚𝑚𝑚𝑚𝑚𝑚 ) and a reduction of the coefficient of variation 𝐶𝐶𝑉𝑉𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 with the increase of the spark advance. Therefore a relationship is derived to express 𝑃𝑃̅𝑚𝑚𝑚𝑚𝑚𝑚 and 𝐶𝐶𝑉𝑉𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 as function of the spark advance and, in turn, to
evaluate the distribution of 𝐶𝐶𝑘𝑘 to be assumed in the two-zone combustion model.
Fig. 5. MAPO probability density functions Taking advantage of the statistical analysis, the randomness of the knocking phenomenon is described as a function of the 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 : individual MAPO values can be randomly identified
4.3 Knock Intensity Model Validation
by a specific log-normal distribution.
The occurrence of knocking in the experimental pressure cycles is assumed when the calculated MAPO exceeds the threshold value, that is set to 1.25, 1.75, 2 for the test cases 1, 2, 3, respectively.
Figure 6 shows the results in terms of MAPO mean and RMS prediction, evidencing a good agreement between experimental and simulated data. Starting from these results it is possible to calculate the individual MAPO values shown in Figure 7.
Figure 4 shows the pressure signal processed by the band-pass filter mentioned in section 4.1. The figure evidences the knock onset (𝜃𝜃𝐾𝐾𝐾𝐾,𝑒𝑒𝑒𝑒𝑒𝑒 ) that corresponds to the crank angle in which the MAPO exceeds the threshold value. 294
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295
methodology (𝑘𝑘𝑘𝑘𝑠𝑠𝑠𝑠𝑠𝑠 ), evidencing the good agreement achieved. Figure 8 reports a flow diagram of the main steps of the proposed model based methodology to estimate the KLSA.
Fig. 6. Comparison between simulated and experimental mean values and RMS of MAPO at 2500 rpm. 𝜃𝜃𝑆𝑆𝑆𝑆 = 11.55 [𝑑𝑑𝑑𝑑𝑑𝑑 𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵]
Fig. 8. Schematic procedure for knock detection The data related to the operating condition to be studied are supplied as input to the two-zone combustion model. In particular, according to the current spark advance 𝜃𝜃𝑆𝑆𝑆𝑆 , the 𝐶𝐶𝑘𝑘 distribution which most suitably describes the combustion process and the cyclic dispersion is defined. The outputs of the two-zone model are supplied to the autoignition equation of the unburnt mixture. In case of knocking cycles, the knock onset 𝜃𝜃𝐾𝐾𝐾𝐾,𝑒𝑒𝑒𝑒𝑒𝑒 is used to evaluate the pressure gradient related to the knocking effect ∆𝑝𝑝𝐾𝐾𝐾𝐾 .
Fig. 7. Comparison between simulated and experimental MAPO at 2500 rpm. 𝜃𝜃𝑆𝑆𝑆𝑆 = 11.55 [𝑑𝑑𝑑𝑑𝑑𝑑 𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵] The results show that the method allows estimating MAPO with satisfactory agreement with the experimental data, evidencing an effective description of the stochastic nature of the knocking phenomenon.
By exploiting these results and the statistical data, it is possible to define the percentage of knocking cycles 𝑘𝑘𝑘𝑘. Depending on this percentage, the spark advance is reduced or increased, repeating the process until the target imposed on the percentage of knocking cycles is reached. The spark advance that complies with this constraint is identified as KLSA.
Table 2 reports, for the various operating conditions, the percentages of knocking cycles, detected from the experimental data (𝑘𝑘𝑘𝑘𝑒𝑒𝑒𝑒𝑒𝑒 ) and from the model-based
Table 2. Experimental and simulated percentages of knocking cycles for the three operating conditions Operating conditions 𝜽𝜽𝑺𝑺𝑺𝑺 [𝒅𝒅𝒅𝒅𝒅𝒅 𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩] 𝒌𝒌𝒌𝒌𝒆𝒆𝒆𝒆𝒆𝒆 [%] 𝒌𝒌𝒌𝒌𝒔𝒔𝒔𝒔𝒔𝒔 [%]
1 13.05 6.2 5.9
12.2 4.2 3.8
2 11.55 3.3 2.8
25.3 1.6 1.4
5. CONCLUSIONS
24.9 1.3 0.09
3 24.3 0.08 0.06
21.7 3.4 4.1
21.2 2.4 3.2
20.75 2.1 2.8
combustion model that exhibits low computational demand and good reliability.
In this paper a model-based methodology for the prediction of incipient knock conditions is presented. The procedure aimed at estimating the KLSA is based on the use of a two-zone
The estimation of the CCV, that is fundamental for the description of knocking, is accomplished by a relationship between the model parameter 𝐶𝐶𝑘𝑘 and 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚 and 𝐶𝐶𝑉𝑉𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 . The 295
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auto-ignition of the unburnt mixture is evaluated by the criterion proposed by Livengood-Wu, in which the knock onset is established on the basis of the value assumed by an integral function dependent on the ignition delay, evaluated by a single-stage Arrhenius relation.
Development and Identification”, SAE 2003 Transactions - Journal of Engines, 112-3: 1408-1416, 2004. Livengood JC, Wu PC (1955) ‘‘Correlation of auto-ignition phenomena in internal combustion engines and rapid compression machines’’, Symposium (International) on combustion, 5;1955. p. 347–56. Vandersickel A, Boulouchos K, Fikri M, Hartmann M, Schulz C, Starke R, Vogel K, Wright YM (2012) ‘‘The autoignition of practical fuels at HCCI conditions: Highpressure shock tube experiments and phenomenological modeling’’, Fuel. 93. 10.1016/j.fuel.2011.10.062. Galloni E, Fontana G, Staccone S (2014) “Numerical and experimental characterization of knock occurrence in a turbo-charged spark ignition engine”. Energy Conversion and Management 85 (2014) 417–424. Pan J, Shu G, Wei H (2013)‘‘Analysis of onset and severity of knock in SI engine based on in-cylinder pressure oscillations’’, Appl Therm Eng 2013;51:1297–306. Gautam & Babiker, Hassan & Badra, Kalghatgi, Jihad (2015) “A Simple Method to Predict Knock Using Toluene, NHeptane and Iso-Octane Blends (TPRF) as Gasoline Surrogates”. SAE International Journal of Engines. 201501-0757. 10.4271/2015-01-0757. Abraham M, Prakash S (1992) “Cyclic Variations in a Small Two-Stroke Cycle Spark-Ignited Engine - An Experimental Study,” SAE Technical Paper 920427, 1992, doi:10.4271/920427. Andrzej & Haggith, Dale & Sobiesiak, Grzegorz & Szlek, Przybyla (2016) ‘‘Fuelling of spark ignition and homogenous charge compression ignition engines with low calorific value producer gas’’. Energy. 10.1016/ j.energy. 2016.06.036. Frey J, Peyton Jones JC, Spelina J M. (2013) “Characterization of knock intensity distributions: Part 1: statistical independence and scalar measures”, Proceedings of the Institution of Mechanical Engineers, Part D: Journal of automobile Engineering, 228(2) :117-128, 2013.
To assess the knock intensity, a method is proposed that allows describing the stochastic nature of the knocking phenomenon. The experimental validation has been carried out by processing the measured pressure cycles to evaluate the statistical variables related to MAPO (e.g. mean, variance and pdf). The results show a good accuracy in estimating the knock phenomenon in terms of both onset and intensity. The percentages of knocking cycles properly predicted are between the 85% and 95% of the experimental ones. Future developments include the validation of the method in a wider range of engine operating conditions. REFERENCES Reitz RD (2013) “ Directions in internal combustion engine research”, Combust Flame 2013; 160:1-8. Wang Y, Zhen X, Zhu Y (2013) “Study of knock in a high compression ratio SI methanol engine using LES with detailed chemical kinetics” Energy Converse Manage 2013;75:523-31. Dubar B, Leduc P, Ranini A, Monnier G (2003) ‘‘Downsizing of Gasoline Engine:an Efficient Way to Reduce CO2 Emissions’’, Oil Gas Sci. Technol. – Rev.IFP. 58 (2003) 115–127. doi:10.2516/ogst:2003008. Hettinger A Kulzer A (2009) “A new method to detect knocking zones” SAE Internal J Engines 2009; 2:645-65. Arjmandi Tash H, Ettefagh MM, Prrouzpanah V, Sadeghi MH (2008) “Knock detection in spark ignition engines by vibrational analysis of cylinder block: A parametric modeling approach”, Mechanical Systems and Signal Processing Journal, 22, pp. 1495–1514, 2008. Draper CS (1938) ‘‘Pressure waves accompanying detonation in the internal combustion engine’’, J Aeronaut Sci (Inst Aeronaut Sci) 1938;5:219–26. Wu G (2007) ‘‘A real time statistical method for engine knock detection’’, SAE Technical Paper, 2007-01-1507, 2007. Abu-Qudais M. (1996) ‘‘Exhaust Gas Temperature for Knock Detection and Control in Spark Ignition Engine’’, Energy Convers. Mgmt, Vol. 37, No. 9, pp. 1383-1392, 1996. Bellettre J, Brecq G, Tazerout M (2003) ‘‘A New Indicator for Knock Detection in Gas SI Engines’’, International Journal of Thermal Sciences, 42, pp.523-532. 2003. Leppard WR (1982) ‘‘Individual-cylinder knock occurrence and intensity in multi-cylinder engines’’, SAE Technical Paper 820074, 1982. De Bellis V, Minarelli F, Siano D, Teodosio L et al (2015) ‘‘Knock and Cycle by Cycle Analysis of a High Performance V12 Spark Ignition Engine. Part 1: Experimental Data and Correlations Assessment’’, SAE Int. J. Engines 8(5):2015, doi:10.4271/2015-24-2392. Arsie I, Pianese C., Rizzo G (2004) “An Integrated System of Models for Performance and Emissions in SI Engines: 296
ScienceDirect A model based methodology for knock prediction in SI engines A model based methodology for knock IFAC PapersOnLine 52-5 (2019) 291–296prediction A model based methodology for knock prediction in in SI SI engines engines A model based methodology for knock prediction in SI engines B. Rossomando*, C. Fruncillo*, I. Arsie*, M. Comentale*, M. De Cesare** A model based methodology knock predictionM.inDeSI engines B. Rossomando*, C. Fruncillo*,for I. Arsie*, M. Comentale*, Cesare**
B. Rossomando*, C. Fruncillo*, I. Arsie*, M. Comentale*, M. De Cesare** B. Rossomando*, C. Fruncillo*, I. Arsie*, M. Comentale*, M. De Cesare** *Dept. of Industrial Engineering, University of Salerno Fisciano Italy; Engineering, (e-mail: brossomando@ B. Rossomando*, C. Fruncillo*, I. Arsie*, M. Comentale*, M. De Cesare** *Dept. of (SA) Industrial University ofunisa.it). Salerno *Dept. of Industrial Engineering, University of(e-mail: Salerno **Magneti Marelli Powertrain, Bologna Italy Fisciano (SA) Italy; (e-mail: brossomando@ unisa.it). *Dept. of Industrial University ofunisa.it). Salerno Fisciano (SA) Italy; Engineering, (e-mail: brossomando@ [email protected]) **Magneti Marelli Bologna Italyunisa.it). (e-mail: Fisciano (SA) Italy;Powertrain, (e-mail: brossomando@ **Magneti Marelli Powertrain, Bologna Italy (e-mail: [email protected]) *Dept. of Industrial Engineering,Bologna University of(e-mail: Salerno **Magneti Marelli Powertrain, Italy [email protected]) Fisciano (SA) Italy; (e-mail: brossomando@ unisa.it). [email protected]) Marelli Powertrain, Bologna (e-mail: Abstract: In spark-ignition**Magneti engines, knock control represents one ofItaly the most critical issue to reach optimal [email protected]) thermal efficiency. The paper deals with the development of a methodology aimed at evaluating most Abstract: In spark-ignition engines, knock control represents one of the most critical issue to reachthe optimal Abstract: In spark-ignition engines, knock control represents one of the most critical issue to and reachknocking optimal suited spark advance to achieve the right compromise between performance optimization thermal The paper deals knock with the development of one a methodology aimed at evaluating the most Abstract:efficiency. In(KLSA). spark-ignition engines, control represents of the most critical issue to reach optimal thermal efficiency. The paper deals withisthe development of a methodology aimed at evaluating the most occurrence The methodology based on combustion simulation via a two-zone 0D knocking model in suited spark advance to achieve the right compromise between performance optimization and thermal efficiency. The paper deals with the development of a methodology aimed at evaluating the most suited spark advance to achieve the right compromise between performance optimization and knocking which the cycle-by-cycle variation (CCV) is described by a model parameter that impacts on the turbulence occurrence (KLSA). The methodology is based on combustion simulation via a two-zone 0D model in Abstract: In(KLSA). spark-ignition engines, knock represents one of the most critical issue to and reach optimal suitedatspark advance to achieve the right compromise between performance occurrence The methodology is control basedofon combustion simulation viaoptimization a two-zone 0D knocking model in level inlet valve closing. The auto-ignition the unburnt mixture is described by a thermodynamic which the cycle-by-cycle variation (CCV) is described by a model parameter that impacts on the turbulence thermal efficiency. The paper deals(CCV) withisthe development of a methodology aimed at evaluating the most occurrence (KLSA). The methodology on combustion simulation via a two-zone 0D model in which the cycle-by-cycle variation isbased described by aevaluated model parameter that impacts on the turbulence equation derived from literature while knock intensity is by a stochastic approach. The method level atthe inlet valve closing. The the auto-ignition of the by unburnt mixture is described by aonthermodynamic suited spark advance to achieve right compromise between performance optimization and knocking which cycle-by-cycle variation (CCV) is described a model parameter that impacts the turbulence level at evaluating inlet valvethe closing. The auto-ignition ofcycles, the unburnt mixture described by a thermodynamic allows percentage of knocking on ais the spark actuated. The equation derived from literature while knock intensity isdepending evaluated by stochastic approach. Themodel method occurrence (KLSA). The methodology is based combustion simulation via a advance two-zone 0D in level at inlet valve closing. The auto-ignition ofon the unburnt mixture described by aonthermodynamic equation derived from literature while knock intensity iscollected evaluated by aisstochastic approach. The method validation has been carried out vs. experimental data at the engine test rig a 4 cylinders allows evaluating the percentage of knocking cycles, depending on the spark advance actuated. The which the cycle-by-cycle variation (CCV) is described by a model parameter that impacts on the turbulence equation derived from while knock intensity evaluated by athe stochastic approach.actuated. The method allows evaluating the literature percentage of knocking cycles, depending on spark advance The turbocharged byThe comparing predicted and is experimental MAPO. validation hasGDI beenengine, carried out vs. data collected at on the engine rig aonthermodynamic a 4 cylinders level at evaluating inlet closing. auto-ignition the mixture described by allows percentage ofexperimental knockingofcycles, depending the sparktest advance The validation hasvalve beenthe carried out vs. experimental dataunburnt collected at theis engine test rig on actuated. a 4 cylinders turbocharged engine, byFederation comparing and experimental MAPO. Keywords: SI GDI Engine; Combustion Knock Detection; Model-based Calibration andaDiagnostics equation derived from literature while knock intensity is evaluated aElsevier stochastic The method © 2019, IFAC (International of predicted Automatic Control) Hosting by Ltd. All validation has been carried vs.Control; experimental data collected atby the engine testapproach. rig rights on 4reserved. cylinders turbocharged GDI engine, byout comparing predicted and experimental MAPO. allows evaluating the Combustion percentage of knocking cycles, depending on the spark advance The Keywords: SI GDI Engine; Control; Knock Detection; Model-based Calibration andactuated. Diagnostics turbocharged engine, by comparing predicted experimental MAPO. and Keywords: SI Engine; Combustion Knock Detection; Model-based Calibration andaDiagnostics validation has been carried out vs.Control; experimental data collected at the engine test rig on 4 cylinders anomalous combustionCalibration may occurand dueDiagnostics to self-ignition of the Keywords: SI GDI Engine; Combustion Control; Knock Detection; Model-based and turbocharged engine, by comparing predicted experimental MAPO. 1. INTRODUCTION mixture, thus resulting in knocking. anomalous combustion may occur due to self-ignition of the anomalous combustion may occur dueDiagnostics to self-ignition of the 1.SI INTRODUCTION Engine; Combustion Control; Knock Model-based Calibration and The knock represents most critical issue to improve engine In the last Keywords: twenty years the energy question and its impact on Detection; mixture, thus resultingthe inmay knocking. 1. INTRODUCTION anomalous combustion occur due to self-ignition offrom the mixture, thus resulting in knocking. fuel economy and prevents the combustion controlengine the has assumed global importance. 1. INTRODUCTION The knock represents the most critical issue to improve In theenvironment last twenty years the energy question and its impactThe on mixture, thus resulting in knocking. The knock represents the most critical issue to improve engine In the last twenty years the energy question and its impact on achieving the best efficiency, constraints on requirement to reduce greenhouse gasesimportance. has led most fuel economy andthermal prevents the combustion control offrom the environment has the assumed global anomalous combustion may dueimposing to self-ignition the The knock represents the mostoccur critical issue to improve In theenvironment last twenty years energy question and its impactThe on fuel economy and Inprevents the combustion controlengine from the has assumed global importance. The 1. INTRODUCTION the spark advance. order to reduce the occurrence of the governments to set ambitious targets for the improvement of achieving the best thermal efficiency, imposing constraints on requirement to reduce greenhouse gasesimportance. has led most mixture, thus in knocking. fuel economy andthermal prevents the combustion controlandfrom the environment has assumed global The achieving the resulting best efficiency, imposing constraints on requirement to reduce greenhouse gases has led most knocking phenomenon, the enrichment of the mixture the fuel economy (Reitz 2013; Wang et al. 2013). the spark advance. In order to reduce the occurrence of the governments to set ambitious targets for the improvement of The knockthe represents most issue improve engine In the last twenty years thegreenhouse energy question its impact on achieving best angle thermal efficiency, imposing constraints on requirement to non-ideal reduce gases has ledleads most spark advance. Inthe order tocritical reduce the to occurrence of the governments to set ambitious targets for theand improvement of delay of the spark advance arecombustion generally adopted (Leduc In addition, the combustion in the engines to the knocking phenomenon, the enrichment of the mixture and the fuel economy (Reitz 2013; Wang et al. 2013). fuel economy and prevents the control from the environment has assumed global importance. The the spark advance. In order to reduce the occurrence of the governments to set ambitious targets for the improvement of knocking phenomenon, the enrichment of the mixture and fuel economy (Reitz 2013; Wang et al. 2013). et al. 2003; Hettinger et al. 2009), which results in a drastic the production ofnon-ideal other species such as nitrogen oxides, carbon delay of the spark angle advance are generally adopted (Leduc In addition, the combustion in the engines to achieving thespark best angle thermal efficiency, imposing constraints on requirement to reduce gases has ledleads most knocking phenomenon, the enrichment of the mixture and the fuel economy (Reitz 2013;greenhouse Wang and et al.solid 2013). of the advance areunder generally adopted (Leduc In addition, the non-ideal combustion in the engines leads to delay decrease of Hettinger thermal efficiency high load engine monoxide, unburnt hydrocarbons particulates, which et al. 2003; et al. 2009), which results in a drastic the production of other species such as nitrogen oxides, carbon the spark advance. In order to reduce the occurrence of the governments to set ambitious targets for the improvement of delay the spark angleetadvance are which generally adopted In theofnon-ideal combustion in the engines to et al. of 2003; Hettinger al. 2009), results in a (Leduc drastic theaddition, production other species such ashealth. nitrogen oxides,leads carbon conditions. are harmful and dangerous to human decrease of Hettinger thermal etefficiency under high load engine monoxide, unburnt hydrocarbons and particulates, which operating knocking phenomenon, the enrichment of the mixture and the fuel economy (Reitz 2013; Wang et as al.solid 2013). et al. 2003; al. 2009), which results in a drastic the production of other species such nitrogen oxides, carbon decrease of thermal efficiency under high load engine monoxide, unburnt hydrocarbons and solid particulates, which During the development of anareengine, oneadopted of the(Leduc main The goal of research in the automotive field is therefore to limit operating conditions. are harmful and dangerous to human health. delay of the spark angle advance generally In addition, the non-ideal combustion in the engines leads to decrease ofis thermal efficiency under value high of load engine monoxide, unburnt hydrocarbons and health. solid particulates, which conditions. are much harmfulas and dangerous to human objectives to define theof2009), maximum spark as possible theautomotive emissions of pollutants the operating During the development an engine, one ofinthe the main The goal of research in the field is therefore to limit et al. 2003; Hettinger et al. which results a drastic the production ofdangerous other species such ashealth. nitrogen oxides,into carbon operating conditions. are harmful and to human During the development of an engine, one of the main The goal of research in the automotive field is therefore to limit advance to be adopted, in order to maximize thermal efficiency atmosphere, ensuring reduced consumption and at the same objectives is to define the maximum value of the spark as much as possible the emissions of pollutants into the decrease of thermal efficiency under high load engine monoxide, unburnt hydrocarbons and solid particulates, which During theisdevelopment an engine,value one of of the spark main The goal ofasresearch in the field is therefore to limit to define theof maximum the as much possible theautomotive emissions of pollutants into the while preventing intensive knocking. The experimental time maximum performance. The increase of efficiency in objectives advance toconditions. be adopted, in order to maximize thermal efficiency atmosphere, ensuring reduced consumption and at the same operating are harmful and dangerous to human health. objectives is to define the maximum value of the spark as much as possible the emissions of pollutants into the advance to be adopted, in order to maximize thermal efficiency atmosphere, ensuring reduced consumption and at the same identification of this intensive variable, indicated as KLSA (Knockinternal combustion engines, to The meetincrease the increasingly stringent preventing knocking. The experimental time maximum performance. of efficiency in while During the of also an engine, The one of the main The of research in reduced the automotive field is therefore limit advance to bedevelopment adopted, inisorder to maximize thermal efficiency atmosphere, ensuring consumption and at guideline thetosame preventing intensive knocking. experimental timegoal maximum performance. The increase of the efficiency in while limited spark advance), accomplished by an expensive and anti-pollution regulations, has therefore become identification of this variable, also indicated as KLSA (Knockinternal combustion engines, to meet the increasingly stringent objectives is to define the maximum value of the spark as much as possible the emissions of pollutants into the while preventing intensive knocking. The experimental time maximum performance. The increase of efficiency in of this variable, also indicated asmeasurement KLSA (Knockinternal combustion engines, to meet the increasingly stringent identification time consuming process that involves the of to follow. limited spark advance), isorder accomplished by as anKLSA expensive and anti-pollution regulations, has therefore become the guideline advance to be of adopted, inis to maximize efficiency atmosphere, ensuring reduced consumption andthe at guideline the same limited identification thiscycles, variable, also indicated (Knockinternal combustion engines, meet the become increasingly stringent spark advance), accomplished by thermal an expensive and anti-pollution regulations, hastotherefore numerous pressure due to the strong variability of the In the Spark Ignition (SI) engines, various constructive time consuming process that involves the measurement of to follow. while preventing intensive knocking. experimental time maximum performance. The increase of the efficiency in time limited spark advance), isand accomplished byThe an expensive and anti-pollution has therefore become guideline consuming process that involves the measurement of to follow. knocking phenomenon the cycle-by-cycle variation solutions haveregulations, beenengines, developed. The up-to-date technology numerous pressure cycles, due to the strong variability of the In the Spark Ignition (SI) engines, various constructive identification of this variable, also indicated as KLSA (Knockinternal combustion to meet the increasingly stringent time consuming process that the to measurement of to follow. pressure cycles,engines. due involves to the strong variability of this the In the the Spark Ignition (SI) engines, various constructive (CCV) of spark ignition Incycle-by-cycle order overcome where direct in The the up-to-date combustion chamber numerous knocking phenomenon and the variation solutions have beeninjection developed. technology limited spark advance), isand accomplished by an expensive and anti-pollution regulations, has therefore become the guideline numerous pressure cycles, due to the strong variability of the In the Spark Ignition (SI) engines, various constructive knocking phenomenon the cycle-by-cycle variation solutions have been developed. The up-to-date technology issue, model based methods developed to providethis an combined ainjection turbo-compression system, chamber proves (CCV) of spark ignition engines. In order tomeasurement overcome where the with direct in the up-to-date combustion time consuming process that are involves the to of to follow. knocking phenomenon and the In cycle-by-cycle variation solutions beeninjection developed. technology (CCV) of spark ignition engines. order overcome this where thehave direct in The the combustion chamber evaluation of the phenomenon with the minimum cost in terms particularly effective especially when the displacement is issue, model based methods are developed to provide an combined with a turbo-compression system, proves numerous pressure cycles, due to the strong variability of the In the Spark Ignition (SI) engines, various constructive (CCV) of spark ignition engines. In order to to overcome where the direct ainjection in followed the combustion chamber issue, model based methods are developed providethis an combined with turbo-compression system, proves of experimental resources. Thewith aim of this work iscost therefore to reduced: the reduction of the path the flame front, of the phenomenon the minimum in terms particularly effective especially whenup-to-date thebysystem, displacement is evaluation knocking phenomenon and the the cycle-by-cycle variation solutions have beena developed. The technology issue, model based methods are developed to provide an combined with turbo-compression proves evaluation of the phenomenon with minimum cost in terms particularly effective especially when the displacement is provide a methodology for predicting the incipient knock the increase of turbulence in the chamber, the best thermal of experimental resources. The aim of this work is therefore to reduced: the reduction of the path followed by the flame front, (CCV) of spark ignition engines. In order to overcome this where the direct injection in followed the combustion chamber evaluation ofbased theresources. phenomenon minimum inmodel terms particularly effective especially when thebytemperature displacement is of experimental Thewith aim the of this work iscost therefore to reduced: the reduction the path the flame front, conditions, on methods a phenomenological combustion efficiency achieved byof reducing the charge and provide a methodology for predicting the incipient knock the increase of turbulence in the chamber, the best thermal issue, model based are developed to provide an combined with a turbo-compression system, proves of experimental resources. The aim of thisthe work is therefore to reduced: reduction of theinmake path bythe thebest flame front, provide a methodology for predicting incipient knock the increase of turbulence the followed chamber, thermal which takes into account the cycle-by-cycle variation (CCV). the heat the exchange surface, these engines particularly conditions, based on a phenomenological combustion model efficiency achieved byespecially reducing the charge temperature and evaluation of the phenomenon with the minimum cost in terms particularly effective when the displacement is conditions, provide a methodology for predicting the incipient knock the increase of turbulence in the chamber, the best thermal based on a phenomenological combustion model efficiency achieved by reducing the charge temperature and The methodology presentsthe reduced and efficient performing. Themake downsizing allows a reduction which takesbased intoresources. account cycle-by-cycle variation (CCV). the heat and exchange surface, these engines particularly of experimental The aimcomputational of this work isdemand therefore to reduced: the reduction ofreducing the path followed bytemperature the flame front, conditions, on a advance phenomenological combustion model efficiency achieved byconsumption the charge and which cycle-by-cycle variation (CCV). takes into account the the heatspecific exchange surface, make these engines particularly allows setting the spark which guarantee high thermal of the fuel (BSFC) at partial load The methodology presents reduced computational demand and efficient and performing. The downsizing allows a reduction provide a methodology for predicting the incipient knock the increase of turbulence in the chamber, the best thermal which takes into account the cycle-by-cycle variation (CCV). the heat and exchange surface, these (Leduc engines The methodology presents reduced demand and efficient Themake downsizing allowsetparticularly aal. reduction efficiency without theaoccurrence ofcomputational knocking. compared to aperforming. naturally aspirated engine 2003). allows setting the spark advance which guarantee high thermal of the specific fuelbyconsumption (BSFC) at partial load conditions, based on phenomenological combustion model efficiency achieved reducing the chargeallows temperature and allows The methodology presents reduced computational demand and efficient and performing. The downsizing a reduction setting the spark advance which guarantee high thermal of the specific fuel consumption (BSFC) at partial load However, under highsurface, load operating conditions, due to the high efficiency without the occurrence of knocking. compared to a naturally aspirated engine (Leduc etpartial al. 2003). which takes into account the cycle-by-cycle variation (CCV). the heatspecific exchange makeengine these engines particularly allows setting the spark advance which guarantee high thermal of the fuel consumption (BSFC) at load efficiency without the occurrence of knocking. compared to a naturally aspirated (Leduc et al. 2003). pressure and temperature reached inconditions, the combustion However, under high load operating due tochamber, the high efficiency methodology reducedofcomputational efficient The downsizing allows withoutpresents the occurrence knocking. demand and comparedand to aperforming. naturally aspirated engine (Leduc etaal. 2003). However, under high load operating conditions, due toreduction the high The pressure and temperature reached in the combustion chamber, allows setting the spark advance which guarantee high thermal of the specific fuel consumption (BSFC) at partial load However, under high load operating conditions, due to the high pressure and temperature reached in the combustion chamber, 291 Copyright © 2019 IFAC efficiency without the occurrence of knocking. compared to atemperature naturally aspirated (Leduc et al.chamber, 2003). pressure and reached engine in the combustion Copyright 2019 IFAC However,© high load operating conditions, due to the high 291 Copyright ©under 2019 IFAC 291 2405-8963 © 2019, IFAC (International of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. pressure and temperature reached inFederation the combustion chamber, Copyright © 2019 IFAC 291 Peer review under responsibility of International Federation of Automatic Control. 10.1016/j.ifacol.2019.09.047 Copyright © 2019 IFAC 291
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or complete chemical kinetics (Livengood et al. 1955; Vandersickel et al. 2012; Shu et al. 2013).
2. KNOCK DETECTION The occurrence of knocking can be experimentally detected by several methods, among which the most common are those based on the analysis of in-cylinder pressure (Draper 1938), crankcase vibration (Wu 2007; Arjmandi et al. 2008), exhaust gas temperature (Abu-Qudais 1996).
An empirical method is used in the current application, based on the consideration that auto-ignition is not instantaneous but there is a period of "incubation" during which the intermediate oxidation compounds are formed. The time interval between the instant when the mixture reaches pre-set temperature and pressure conditions and the instant when the combustion starts appreciably is called ignition delay 𝜏𝜏.
Some synthetic indices are used to quantify the intensity of knocking and they are related to the in-cylinder pressure signal (MAPO and Kint) or the apparent heat release rate (ROHR and CHR). Among these, MAPO (Maximum Amplitude of Pressure Oscillation) is the most widespread and accepted index, in both academy and industry, (Brecq et al. 2003) and it is often used as a reference when it is necessary to compare the behaviour of different engines in terms of knock. It is defined as the maximum of the absolute value of the filtered in-cylinder pressure signal, evaluated within a time window that includes combustion: 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 = 𝑚𝑚𝑚𝑚𝑚𝑚 |𝑝𝑝𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 |
The ignition delay can be expressed as function of the thermodynamic conditions 𝑝𝑝 and 𝑇𝑇𝑢𝑢 of the unburnt mixture, by means of the following relationship (Kalghatgi et al. 2015): 𝐵𝐵
𝜏𝜏(𝑝𝑝, 𝑇𝑇𝑇𝑇) = 𝐴𝐴 𝑒𝑒 𝑇𝑇𝑢𝑢 𝑝𝑝−𝑛𝑛
(2)
where the constants A, n and B are determined experimentally, according to the characteristics of the fuel. An integral function of auto-ignition delay can thus be calculated by the following equation:
(1)
𝑡𝑡
𝐼𝐼(𝑡𝑡) = ∫0
The calculation of the MAPO is aimed at estimating with sufficient confidence the value of the maximum spark advance that can be adopted without incurring in severe knock (KLSA).
𝑑𝑑𝑑𝑑
𝜏𝜏(𝑝𝑝,𝑇𝑇)
(3)
Considering the whole process, if at the time 𝑡𝑡𝑓𝑓 , in which combustion is completed, the integral is lower than 1, it is possible to assume that knock does not occur (Livengood et al. 1955).
KLSA can be evaluated by a statistical approach (95th percentile) (Leppard 1982; Galloni et al. 2014) or by defining a critical value of MAPO which is an increasing function of the engine speed. In the latter case, for the definition of the KLSA the whole engine operating range has to be explored by varying the spark advance; for each spark advance the percentage of knocking cycles is defined, i.e. those that exceed the established threshold. Starting from this information the spark advance corresponding to the incipient knock is identified (De Bellis et al. 2015).
The index MAPO, relative to the intensity of the knock, has been defined in this work as the sum of two contributions; the former is related to the effect of normal combustion, the second is related to the effect of the proper knock:
𝑀𝑀𝑀𝑀𝑀𝑀𝑂𝑂𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚,𝑠𝑠𝑠𝑠𝑠𝑠 = 𝑘𝑘1 𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑙𝑙𝑙𝑙𝑙𝑙 + 𝑘𝑘2 max(𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 − 1) 𝛥𝛥𝛥𝛥𝐾𝐾𝐾𝐾
(4)
where: - 𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 represents the value of I(t) at the EVO (Exhaust Valve Opening); - 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑙𝑙𝑙𝑙𝑙𝑙 it is the threshold to discriminate a normal combustion from a knocking one, that is defined by the empirical formula 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑙𝑙𝑙𝑙𝑙𝑙 = 𝑟𝑟𝑟𝑟𝑟𝑟/2000. - 𝛥𝛥𝛥𝛥𝐾𝐾𝐾𝐾 represents the pressure gradient caused by knocking. It is estimated assuming that when knock starts occurring, all the unburned fuel in the combustion chamber burns instantaneously; considering a constant volume adiabatic combustion, it is calculated as:
3. KNOCKING MODELING In order to adequately describe the knock phenomenon, in terms of onset and intensity, the first step is to identify a modelling approach that allows representing the processes that influence the knock, i.e. combustion and cycle- by- cycle variation. In this work the combustion process simulation is performed by a two-zone model (Arsie et al., 2004), that was previously validated vs. the engine under study. The CCV is taken into account by the model parameter 𝐶𝐶𝑘𝑘 that describes the level of turbulence at the inlet valve closing (IVC). This parameter allows characterizing the combustion process in terms of combustion speed, maximum pressure 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚 and related angular position 𝜃𝜃𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 .
𝛥𝛥𝛥𝛥𝐾𝐾𝐾𝐾 =
𝑄𝑄KO (𝑘𝑘−1) 𝑉𝑉𝐾𝐾𝐾𝐾
(5)
in which 𝑉𝑉𝐾𝐾𝐾𝐾 is the volume of the combustion chamber when the knock appears (KO: knock onset); k is the ratio between the specific heats of the mixture; 𝑄𝑄KO represents the quantity of chemical energy released when the mixture burns, defined as:
In order to identify the start of knock, it is mandatory to evaluate the ignition delay of the unburnt mixture. There are several models of the ignition delay ranging from simple empirical expressions to complex formulations with reduced
𝑄𝑄KO = (1 − 𝑥𝑥𝑏𝑏,𝐾𝐾𝐾𝐾 ) 𝑚𝑚𝑓𝑓 𝐻𝐻𝑖𝑖 292
(6)
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where 𝑥𝑥𝑏𝑏,𝐾𝐾𝐾𝐾 indicates the burnt fraction at the beginning of the knock; 𝑚𝑚𝑓𝑓 is the amount of fuel in the combustion chamber at the beginning of the cycle; 𝐻𝐻𝑖𝑖 it is the lower heating value of the fuel. - 𝑘𝑘1 and 𝑘𝑘2 are model parameters to be tuned.
kHz is then defined by means of a frequency domain analysis. Once the signal has been filtered, the MAPO is evaluated from the maximum value of the signal module. The pressure cycle without the knocking effect is achieved by applying a low pass filter (low pass LP) with a cut-off frequency of 10 kHz that allows purging the signal from those frequencies related to knocking (Galloni et al. 2014; Brecq et al. 2003).
This approach provides a value of the average MAPO, because, given the uncertainty of the combustion process and knocking phenomenon, more cycles with the same level of 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 can be characterized by different MAPO values.
4.2 Combustion and CCV Model Validation
For this reason, the model is initially tuned considering the mean MAPO values, evaluated experimentally by means of a statistical analysis of the experimental data. In order to describe the randomness of the knocking phenomenon, in addition to the knowledge of the average MAPO, a further relation has to be identified that expresses the standard deviation of the experimental data. This relationship is very similar to (eq. 4) and is dependent on two further parameters 𝑘𝑘3 and 𝑘𝑘4 : 𝑅𝑅𝑅𝑅𝑆𝑆𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀,𝑠𝑠𝑠𝑠𝑠𝑠 = 𝑘𝑘3 𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑙𝑙𝑙𝑙𝑙𝑙 + 𝑘𝑘4 max(𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒 − 1) 𝛥𝛥𝛥𝛥𝐾𝐾𝐾𝐾
293
Model validation is accomplished by considering the average pressure cycle for each operating condition. The parameter 𝐶𝐶𝑘𝑘 is identified by a least square minimization of the following error function: 𝑝𝑝𝑠𝑠𝑠𝑠𝑠𝑠,𝜃𝜃 − 𝑝𝑝𝑒𝑒𝑒𝑒𝑒𝑒,𝜃𝜃
𝑓𝑓 = √( ∑𝑁𝑁 𝜃𝜃=1 ( 1 2
1
𝑁𝑁
𝑝𝑝𝑒𝑒𝑒𝑒𝑒𝑒,𝜃𝜃
2
) )+
1 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑠𝑠𝑠𝑠𝑠𝑠 − 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑒𝑒𝑒𝑒𝑒𝑒 2
𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑒𝑒𝑒𝑒𝑒𝑒
(8)
where 𝑝𝑝𝑠𝑠𝑠𝑠𝑚𝑚,𝜃𝜃 and 𝑝𝑝𝑒𝑒𝑒𝑒𝑒𝑒,𝜃𝜃 are the simulated and experimental in-
(7)
cylinder pressure, respectively, while 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑠𝑠𝑠𝑠𝑠𝑠 and 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑒𝑒𝑒𝑒𝑒𝑒 are
4. EXPERIMENTAL ANALYSIS AND VALIDATION
the corresponding maximum values.
The experimental data are measured at the test rig on a production 4 cylinders, 1.4 liters, turbo-charged GDI engine.
Figure 1 shows a comparison between experimental and simulated in-cylinder pressure for three cycles collected in the same engine operating condition (i.e. test case1), corresponding to the average, minimum and maximum cycles of the CCV distribution.
The data refer to three incipient knock conditions at high load operation and engine speed of 2500, 3500 and 4000 rpm (Tab. 1). Table 1. Engine operating conditions investigated. Test case
1
2
3
Speed [rpm]
2500
3500
4000
SOI [BTDC]
275
308
319
ϑSA [BTDC]
13/12.2/11.5
25.3/24.9/24.3
21.7/21.2/ 20.7
The data were collected by continuously imposing a slight variation of the spark advance (𝜃𝜃𝑆𝑆𝑆𝑆 ) in order to identify the one characterized by the best compromise between high thermal efficiency (high 𝜃𝜃𝑆𝑆𝑆𝑆 ) and knock prevention (low 𝜃𝜃𝑆𝑆𝑆𝑆 ).
Fig. 1. Comparison between simulated and experimental pressure cycle at 2500 rpm. 𝜃𝜃𝑆𝑆𝑆𝑆 = 11.55 [𝑑𝑑𝑑𝑑𝑑𝑑 𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵]
Figure 2 shows the 𝐶𝐶𝑘𝑘 parameter distributions obtained experimentally for the test case 1; the figure evidences the different distributions achieved according with the spark advance variation and the relationship between 𝐶𝐶𝑘𝑘 and the peak pressure value. Each 𝐶𝐶𝑘𝑘 distribution is related to the corresponding distribution of 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚 ; therefore, considering that this set of data can be obtained from the average value 𝑃𝑃̅𝑚𝑚𝑚𝑚𝑚𝑚 and the coefficient of variation 𝐶𝐶𝑉𝑉𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 , it is possible to design a
4.1 Signal Filtration The in-cylinder pressure data have to be suitably processed to define the MAPO and the pressure cycle without the effect of knocking, that is needed to validate the model of combustion and knock. To evaluate MAPO, the signal acquired by the transducer is windowed in a range from the TDC (Top Dead Center) to 60 deg ATDC (After Top Dead Center); subsequently it is filtered through a band-pass filter containing the primary knock frequencies. The range of characteristic frequencies of 10-90 293
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polynomial regression to calculate the distribution of 𝐶𝐶𝑘𝑘 as a function of 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚 .
Fig. 4. Identification of MAPO and 𝜃𝜃𝐾𝐾𝐾𝐾,𝑒𝑒𝑒𝑒𝑒𝑒 Fig. 2. 𝐶𝐶𝑘𝑘 distributions as function of 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚
The whole set of data is divided into a series of pressure intervals containing a number of cycles sufficient for the description of the knocking phenomenon. Within each interval the MAPO has been analysed in terms of average value and standard deviation. The analysis allows defining, for each pressure interval, the corresponding MAPO probability density functions (PDF). As it is shown in figure 5, the PDF of MAPO can be described by a log-normal function due to the non-linearity of the kinetic mechanisms that control the auto-ignition (Spelina et al. 2013). The results show that by increasing the level of pressure, mode, average value and median of each single distribution increase, therefore the intensity of the knocking phenomenon is directly related to its randomness.
Figure 3 shows the experimental distributions of 𝑝𝑝𝑚𝑚𝑎𝑎𝑎𝑎 for the three spark advance values actuated in the test case 1.
Fig. 3. Probability density functions of 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚 As expected (De Bellis et al. 2015; Abraham et al. 1992; Przybyla et al. 2016), the figure exhibits an increase of the maximum average pressure (𝑃𝑃̅𝑚𝑚𝑚𝑚𝑚𝑚 ) and a reduction of the coefficient of variation 𝐶𝐶𝑉𝑉𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 with the increase of the spark advance. Therefore a relationship is derived to express 𝑃𝑃̅𝑚𝑚𝑚𝑚𝑚𝑚 and 𝐶𝐶𝑉𝑉𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 as function of the spark advance and, in turn, to
evaluate the distribution of 𝐶𝐶𝑘𝑘 to be assumed in the two-zone combustion model.
Fig. 5. MAPO probability density functions Taking advantage of the statistical analysis, the randomness of the knocking phenomenon is described as a function of the 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚,𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 : individual MAPO values can be randomly identified
4.3 Knock Intensity Model Validation
by a specific log-normal distribution.
The occurrence of knocking in the experimental pressure cycles is assumed when the calculated MAPO exceeds the threshold value, that is set to 1.25, 1.75, 2 for the test cases 1, 2, 3, respectively.
Figure 6 shows the results in terms of MAPO mean and RMS prediction, evidencing a good agreement between experimental and simulated data. Starting from these results it is possible to calculate the individual MAPO values shown in Figure 7.
Figure 4 shows the pressure signal processed by the band-pass filter mentioned in section 4.1. The figure evidences the knock onset (𝜃𝜃𝐾𝐾𝐾𝐾,𝑒𝑒𝑒𝑒𝑒𝑒 ) that corresponds to the crank angle in which the MAPO exceeds the threshold value. 294
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methodology (𝑘𝑘𝑘𝑘𝑠𝑠𝑠𝑠𝑠𝑠 ), evidencing the good agreement achieved. Figure 8 reports a flow diagram of the main steps of the proposed model based methodology to estimate the KLSA.
Fig. 6. Comparison between simulated and experimental mean values and RMS of MAPO at 2500 rpm. 𝜃𝜃𝑆𝑆𝑆𝑆 = 11.55 [𝑑𝑑𝑑𝑑𝑑𝑑 𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵]
Fig. 8. Schematic procedure for knock detection The data related to the operating condition to be studied are supplied as input to the two-zone combustion model. In particular, according to the current spark advance 𝜃𝜃𝑆𝑆𝑆𝑆 , the 𝐶𝐶𝑘𝑘 distribution which most suitably describes the combustion process and the cyclic dispersion is defined. The outputs of the two-zone model are supplied to the autoignition equation of the unburnt mixture. In case of knocking cycles, the knock onset 𝜃𝜃𝐾𝐾𝐾𝐾,𝑒𝑒𝑒𝑒𝑒𝑒 is used to evaluate the pressure gradient related to the knocking effect ∆𝑝𝑝𝐾𝐾𝐾𝐾 .
Fig. 7. Comparison between simulated and experimental MAPO at 2500 rpm. 𝜃𝜃𝑆𝑆𝑆𝑆 = 11.55 [𝑑𝑑𝑑𝑑𝑑𝑑 𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵] The results show that the method allows estimating MAPO with satisfactory agreement with the experimental data, evidencing an effective description of the stochastic nature of the knocking phenomenon.
By exploiting these results and the statistical data, it is possible to define the percentage of knocking cycles 𝑘𝑘𝑘𝑘. Depending on this percentage, the spark advance is reduced or increased, repeating the process until the target imposed on the percentage of knocking cycles is reached. The spark advance that complies with this constraint is identified as KLSA.
Table 2 reports, for the various operating conditions, the percentages of knocking cycles, detected from the experimental data (𝑘𝑘𝑘𝑘𝑒𝑒𝑒𝑒𝑒𝑒 ) and from the model-based
Table 2. Experimental and simulated percentages of knocking cycles for the three operating conditions Operating conditions 𝜽𝜽𝑺𝑺𝑺𝑺 [𝒅𝒅𝒅𝒅𝒅𝒅 𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩] 𝒌𝒌𝒌𝒌𝒆𝒆𝒆𝒆𝒆𝒆 [%] 𝒌𝒌𝒌𝒌𝒔𝒔𝒔𝒔𝒔𝒔 [%]
1 13.05 6.2 5.9
12.2 4.2 3.8
2 11.55 3.3 2.8
25.3 1.6 1.4
5. CONCLUSIONS
24.9 1.3 0.09
3 24.3 0.08 0.06
21.7 3.4 4.1
21.2 2.4 3.2
20.75 2.1 2.8
combustion model that exhibits low computational demand and good reliability.
In this paper a model-based methodology for the prediction of incipient knock conditions is presented. The procedure aimed at estimating the KLSA is based on the use of a two-zone
The estimation of the CCV, that is fundamental for the description of knocking, is accomplished by a relationship between the model parameter 𝐶𝐶𝑘𝑘 and 𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚 and 𝐶𝐶𝑉𝑉𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 . The 295
2019 IFAC AAC 296 Orléans, France, June 23-27, 2019
B. Rossomando et al. / IFAC PapersOnLine 52-5 (2019) 291–296
auto-ignition of the unburnt mixture is evaluated by the criterion proposed by Livengood-Wu, in which the knock onset is established on the basis of the value assumed by an integral function dependent on the ignition delay, evaluated by a single-stage Arrhenius relation.
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To assess the knock intensity, a method is proposed that allows describing the stochastic nature of the knocking phenomenon. The experimental validation has been carried out by processing the measured pressure cycles to evaluate the statistical variables related to MAPO (e.g. mean, variance and pdf). The results show a good accuracy in estimating the knock phenomenon in terms of both onset and intensity. The percentages of knocking cycles properly predicted are between the 85% and 95% of the experimental ones. Future developments include the validation of the method in a wider range of engine operating conditions. REFERENCES Reitz RD (2013) “ Directions in internal combustion engine research”, Combust Flame 2013; 160:1-8. Wang Y, Zhen X, Zhu Y (2013) “Study of knock in a high compression ratio SI methanol engine using LES with detailed chemical kinetics” Energy Converse Manage 2013;75:523-31. Dubar B, Leduc P, Ranini A, Monnier G (2003) ‘‘Downsizing of Gasoline Engine:an Efficient Way to Reduce CO2 Emissions’’, Oil Gas Sci. Technol. – Rev.IFP. 58 (2003) 115–127. doi:10.2516/ogst:2003008. Hettinger A Kulzer A (2009) “A new method to detect knocking zones” SAE Internal J Engines 2009; 2:645-65. Arjmandi Tash H, Ettefagh MM, Prrouzpanah V, Sadeghi MH (2008) “Knock detection in spark ignition engines by vibrational analysis of cylinder block: A parametric modeling approach”, Mechanical Systems and Signal Processing Journal, 22, pp. 1495–1514, 2008. Draper CS (1938) ‘‘Pressure waves accompanying detonation in the internal combustion engine’’, J Aeronaut Sci (Inst Aeronaut Sci) 1938;5:219–26. Wu G (2007) ‘‘A real time statistical method for engine knock detection’’, SAE Technical Paper, 2007-01-1507, 2007. Abu-Qudais M. (1996) ‘‘Exhaust Gas Temperature for Knock Detection and Control in Spark Ignition Engine’’, Energy Convers. Mgmt, Vol. 37, No. 9, pp. 1383-1392, 1996. Bellettre J, Brecq G, Tazerout M (2003) ‘‘A New Indicator for Knock Detection in Gas SI Engines’’, International Journal of Thermal Sciences, 42, pp.523-532. 2003. Leppard WR (1982) ‘‘Individual-cylinder knock occurrence and intensity in multi-cylinder engines’’, SAE Technical Paper 820074, 1982. De Bellis V, Minarelli F, Siano D, Teodosio L et al (2015) ‘‘Knock and Cycle by Cycle Analysis of a High Performance V12 Spark Ignition Engine. Part 1: Experimental Data and Correlations Assessment’’, SAE Int. J. Engines 8(5):2015, doi:10.4271/2015-24-2392. Arsie I, Pianese C., Rizzo G (2004) “An Integrated System of Models for Performance and Emissions in SI Engines: 296