- Email: [email protected]
PLC controlled single cylinder diesel-LPG engine
Fuel 130 (2014) 273–278
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
PLC controlled single cylinder diesel-LPG engine Alp Tekin Ergenç ⇑, Deniz Özde Koca Yildiz Tecnical University, Mechanical Engineering Department, IC Engines Laboratory, Turkey
h i g h l i g h t s Electronic injection system increases the quality of the combustion. We controlled all injectors by Programmable Logic Controller. A PLC is an unorthodox solution for engine control systems. The maximum cylinder pressure raises with the LPG addition. Reducing the injection advance before the TDC caused lower maximum power.
a r t i c l e
i n f o
Article history: Received 10 December 2013 Received in revised form 3 April 2014 Accepted 6 April 2014 Available online 24 April 2014 Keywords: Diesel engine LPG Injection Advance PLC
a b s t r a c t The main purpose of this work is to convert the mechanical injection system of a single cylinder diesel engine to an electronically controlled dual-fuel system. The new system consist two different injectors. First injector supplies the LPG (liquefied petroleum gas) , the other one supplies the diesel. LPG is supplied via a port fuel injection system located in the intake port of the engine and the diesel injected directly into the combustion chamber before top dead center (TDC). All injectors were controlled by Programmable Logic Controller (PLC). After the adaptation and tests, the single cylinder Lombardini LDA 450 type diesel engine was modified to a high pressured PLC controlled dual-fuel research engine. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Environmental concerns and depletion in petroleum resources have forced researchers to concentrate on finding alternatives to conventional petroleum fuels. A lot of experimental efforts are focused on simultaneous achievement of high energy efficiency and reduction of harmful emissions [7]. The emission problem divided into two parts. The first is the engine and the old car population; the second is the fuel. Due to developments in engine technology, the emission pollutants levels are high because of the fuel specifications. According to the new regulations the fuel specifications are more important for the vehicles [23]. At this point, the use of gaseous fuels in I.C. engines has long been considered as a possible method for reducing emissions while maintaining engine performance and efficiency [8]. LPG is considered, to be one of the most proficient alternative fuels not only as a replacement for petroleum fuel but also as a basis of reducing NOx, soot and particulate matter. LPG has a high octane rating and hence ⇑ Corresponding author. Tel.: +90 2123832835; fax: +90 2122616659. E-mail address: [email protected] (A.T. Ergenç). http://dx.doi.org/10.1016/j.fuel.2014.04.016 0016-2361/Ó 2014 Elsevier Ltd. All rights reserved.
well appropriate for S.I. engine. But when LPG is burnt in the usual diesel engine there is a difficulty in self-ignition because of its lower cetane number [10]. Nowadays, LPG becomes more attractive at our country, because of environmental benefits in terms of emissions and it is cheaper unit price. In general, SI (spark ignition) engine powered old cars fuel system changed into dual fuel (LPG/Gasoline) system. Recent years, due to the higher petrol prices and taxes, the unit price of gasoline and diesel rises dramatically. High diesel fuel price, have forced the issue of the use of LPG at diesel engine. Since the early 1930’s, there is a fluctuating interest in the research of compression engines operating on dual fuels. Recently, dual fuel engines are receiving more interest from many scientists due to many reasons including the national concerns of the liquid fuels limited resources, the environmental issues and the need to use a reliable, durable and efficient engine [3]. The dual fuel engines studies focuses on utilizing the gaseous fuels like natural gas, hydrogen and LPG as primary fuel in compression engines, due to the higher ignition temperature of this fuels. This primary fuels increases the mixture temperature [4]. Furthermore, because of the higher octane number of the gaseous
274
A.T. Ergenç, D.Özde Koca / Fuel 130 (2014) 273–278
fuels, it can be used in conventional high compression engine with minor modifications, with comparable efficiencies to diesel fuel [3] According to Yoong and Watkins, [9] a higher thermal efficiency and therefore, improved fuel economy can be obtained from internal combustion engines running on LPG as opposed to unleaded gasoline. This is because LPG has a higher octane number, typically 112 Research Octane Number for pure propane, which prevents the occurrence of detonation at high engine compression ratio [5]. Homoyer et al. [6] states that there is a penalty in power output when using LPG compared to gasoline due to the displacement of some of the inspired air by the fuel gas whose volume is much greater than that of its elated liquid. In dual fuel compressed ignition engines operating with LPG as primary fuel and a pilot amount of diesel fuel as an ignition source, the LPG is induced along with the intake air and is compressed like in a conventional diesel Engine. The mixture of air and LPG does not auto-ignite due to its high auto-ignition temperature. A Small amount of diesel fuel is injected near the end of the compression stroke to ignite the gaseous mixture. Poonia et al. [11] performed experiments on LPG-diesel dual fuel engine at various intake temperature and pilot quantities. It was found that by increase in the concentration of the gaseous primary fuel, ignition delay increases considerably. At higher load condition, the combustion of the gaseous fuel takes place by flame propagation after ignition of pilot fuel. Ganesan and Ramesh [12] used LPG as the primary fuel and diesel as pilot fuel. The brake thermal efficiency was increased from 35% in the diesel mode to 37% in dual fuel mode at full load condition due to rise in the combustion rate. However, at lower load condition and with high diesel substitution, brake thermal efficiency reduces and hydrocarbons and CO levels increase. It is also noted that NOx levels reduce in the dual fuel mode up to 60% of full load condition. The smoke emission reduces from 1.3 Bosch Smoke Units (BSU) to 0.5 (BSU) with dual fuel mode at full load. The ignition delay period increases by 2 °CA (crank angle) and the peak pressure decreases under light load and high diesel substitutions conditions. Saleh [2] studied the effects of LPG compositions on the exhaust emissions of the dual fuel compression engine under different engine conditions. This study reported that LPG with 70% propane blend is showing a similar performance compared to the conventional diesel engine. For the 70% propane blend, NOx and SO2 emission decreased by 27–69% meanwhile, the CO emission decreased by 15.7% compared to the conventional diesel engine. A high-quality formation for combustion is achieved by mixing of pulverized fuel drops and the air inside the cylinder [13]. In this matter, injection parameters such as timing and period of injection, injection pressure and number of the injection beams affect quality of combustion and mixture formation. At this point, injection system has an important role on mixture formation. Injection timing and period determines the beginning of the combustion in terms of crankshaft angle. Commercial single cylinder engines are produced with mechanical fuel injection systems, which have predetermined parameters. Thus the effects of different operational parameters such as advance angle, injection pressure, and duration and phase numbers cannot be tested. In a test engine, injectors should be controlled depending on the operational parameters of the engine (speed, gas position, etc.). In alternative fuel studies, the injection system parameters like pressure, injection advance, and injection character must be controllable. In general, single cylinder diesel test engines have mechanical unit pump systems and this system have no changeable parameters. Utilizing common-rail injection instead of mechanical injection pump can control timing and period. Common-rail mechanisms provide us to employ efficient and flexible control schemes on the injection system.
Application of high-pressure injection systems increases amount of fuel injection per crankshaft angle and also shortens the ignition delay. Naturally this delay has a minimum value that cannot be breached. The amount of the fuel injected into cylinder increases with the pressure till the ignition starts and this leads to higher levels of NOx and noise. In order to compensate these problems pre-injection technique is utilized. NOx and noise levels diminish with this method [14–18]. In addition, high-pressure injection improves specific fuel consumption and particle emission levels [19,20]. As a summary, in a test engine advance angle, duration and number of injections are the parameters subject to be adjusted to discover best blending ratios of alternative fuels. In addition, a measurement system is vital to measure torque output, speed, temperature, airflow rate, combustion pressure and emissions. The data collected from the system associated with control parameters and corresponding measurements can be used for system identification of the test engine and therefore; optimal operational region would be determined. In dual-fuel operation, LPG fuel injected with a system located to the intake port of the DI (direct injection) diesel engine and diesel fuel injected directly into the combustion chamber with an electromagnetic injector before top dead center. All injectors were controlled by Programmable Logic Controller. In dual fuel mode, with gas mixed into the air intake while liquid diesel is injected as normal, but a reduced rate [26]. 2. Engine management The test engine system for alternative fuels consists of three main parts. First part is the engine and its controller. Second part is the fuel system including common-rail pressure line and low pressure fuel line (dual fuel). Finally, the third part is the measurement system that includes all the sensors and transducers, which provides feedback from all the operational quantities listed above. A Single cylinder diesel engine is coupled with a DC motor over a belt pulley mechanism with a ratio of 1:2. A two quadrant driver is attached to DC motor. In the first quadrant, it operates as a starter motor for the engine and in the second one, as a generator to load the engine. 2.1. Engine Controller Unit (ECU) Electronic engine controls based on real time diagnosis of combustion process can significantly help in complying with the exhaust emission regulations and fuel consumption. Information on the combustion efficiency may provide a strong tool regarding engine operation and may be profitably used for closed-loop electronic engine controls [24,25]. In an electronically controlled engine system a micro-controller based controller is necessary to collect data and generate necessary signals to drive the injectors (LPG and diesel) in real-time. Programmable Logic Controllers (PLC), which particularly developed for industrial automation, can be utilized for controlling single cylinder engine. PLC have real-time operating systems, timers and counters crucial for real-time control systems. Another advantage of is that PLCs are relatively economical resolution for control applications. PLC, as an ECU, collects data from sensors such as crankshaft encoder, pressure and temperature transducers, then generates driving signals of the injectors. Siemens S7-200 series CPU224 PLC is suitable with its 14 digital inputs and 10 digital outputs. An analog module is attached to the PLC for analog data acquisition [22]. In the PLC used as the controller, there are precision timers for injection timing, high-speed counters for counting incremental
275
A.T. Ergenç, D.Özde Koca / Fuel 130 (2014) 273–278
encoder pulses to achieve crankshaft position and high-speed pulse generators for injection signals. A TD200 HM interface is utilized for entering the position of virtual gas pedal position, injection advance angle values and displaying user data such as rpm, common-rail pressure value. Addition to displaying data, HM interface is used to switch operation modes between constant speed control mode and injector calibration mode. An IVO brand incremental encoder, which has 360 lines/rev, is used to assess the position of the crankshaft. Its zero position is set to top dead center of piston. TDC is determined by visual measurement of the piston after cylinder head is opened. It is marked when the piston altered its direction during its reciprocating motion when both valves (intake and exhaust) are closed. It is essential to detect exact position of the crankshaft in order to provide right injection advance angle for the engine. A single degree offset from the actual crankshaft angle would change the characteristics of the combustion in the engine drastically. Incremental encoder is connected to two high-speed counters of the PLC to trigger event-based interrupt subroutines in order to generate two different fuel injections with two different injectors. Event-based interrupt subroutines run when counters reach to preset values. In the interrupt, pulse width modulated injection signals are generated from the high-speed output of the PLC. In the time-based interrupt cycle of the PLC, encoder signals are used to compute the speed of the engine by the number of the pulses per sampling time.
2.2. Dual fuel system Electronically controlled fuel injection system should provide same performance from the engine, so the duration of injection of the electromagnetic injector is subject to be correlated with the SFC. The step after determination of SFC for mechanical injector is to calibrate the electromagnetic injector for the same operation regime. Shortly, it is necessary to determine the amount of fuel injected per time when injector is open. Naturally, the amount is function of not only injection duration but also common-rail pressure. After the mechanical tests, the diesel engine was modified for dual fuel application. Common-rail fuel injection system (900– 1600 bar of injection pressure) and LPG injection system were adapted to the test engine. The LPG injector positioned directly to the upstream of intake valve. Specifications of the test engine are listed in the Table 1. The test bed is illustrated in Fig. 1. The pressure of the common-rail (diesel) is generated by a radial pressure pump with three pistons. In the test bed, the pump is driven by a 3HP three-phase induction motor. The diesel fuel supplied from the fuel tank. The LPG fuel system is more basic than the common-rail. An ordinary LPG tank, LPG filter, regulator, and a rail were used to supply the LPG to the injector. The pressure in common-rail is controlled for the reference values between 200 and 1600 bars. These values are selected to test injector behavior and also variation of combustion quality depending on the pressure. In radial pressure pumps, output pressure is
Table 1 Technical specifications of LDA 450. Total displacement Number of cylinders Injection timing (electronically) Bore Stroke Max. torque at 2200 rpm Max. power at 3000 rpm
454 cm3 Single Changeable – BTDC 85 mm 80 mm 28.5 Nm 7.5 kW
High pressure Diesel pump Diesel injector
LPG injector
DC Motor
Fig. 1. LPG ınjected PLC controlled single cylinder diesel engine test bed.
controlled via PWM signal, which switches the plungers on and off. A pressure transducer is utilized for feedback. 2.3. Injector calibration The common rail injector’s calibration experiments are conducted for 900–1600 bars by 100 bars increments without combustion. In the preliminary experiments, substantial variations of injection characteristics are recorded depending on fuel temperature. In order to avoid these variations, a cooler is utilized to keep the temperature of the fuel below 40 C. Sartorius brand precision scale is used to measure the weight of the fuel injected for certain amount of injection duration. For common rail experiment, injector is triggered 1000 times into a container and the weight of the diesel is measured. The LPG injector’s calibration experiments are conducted for standard pressure at different opening durations. The injector is triggered several times .The number of LPG injections is counted at different opening durations to spend 10 g of LPG Fuel. After the calibration, the relation between the power output and injection duration is determined. The next step is to establish control of the engine with a microcontroller-based system. 2.4. Engine control algorithm It is well known that in diesel engines, combustion occurs when fuel–air mixture is compressed tightly. The main factors in this operation are the quality of the fuel–air mixture and compression ratio. Due to mechanical constraints compression ratios is kept constant. On the other hand, mixture formation is a parameter that we can manipulate. In the conventional diesel engines, which have no turbo charger, there are four parameters that can be controlled; advance angle, amount of injected fuel, pressure of the injection and the number of the injection phases. The controller of the test unit should be able manipulate all these parameters. As mentioned earlier, a PLC is an economic resolution as a controller. It has all essential units for creating an ECU. It has analog inputs to read feedback, high-speed counters to detect encoder outputs for measuring crank-shaft angle, event-based interrupt capability for injection algorithms, and high-speed digital outputs for generating PWM (Pulse width modulation) signals for pressure control and PTO (Pulse train output)) signals for injector control. It also has real-time clock, which is essential for real-time control systems [21,22]. The flowchart of the control algorithm is displayed in Fig. 2a. Injection is started at advance angle from TDC and continued for
276
A.T. Ergenç, D.Özde Koca / Fuel 130 (2014) 273–278
Fig. 2. (a) Diesel engine control algorithm and (b) control and feedback signals.
Fig. 3. Experimental set-up.
A.T. Ergenç, D.Özde Koca / Fuel 130 (2014) 273–278
277
Power
8 7,8 7,6
kW
7,4 7,2 7 6,8 6,6 6,4 6,2
DİESEL+10%LPG
DİESEL+%20%LPG
DİESEL+%25%LPG
Advance 20
DİESEL 7,11
7,35
7,7
7,81
Advance17
6,82
7,22
7,66
7,64
Fig. 4. Power curves of diesel and dual operations.
an amount of time (injection duration). Both of these values are controlled. In Fig. 2b, encoder signal for bottom dead center (BDC), injection signals and pressure in the cylinder is displayed. The encoder signal from BDC is used, because the high-speed counter is reset at TDC. As it is visible, the inner pressure of the cylinder increases when the piston reaches to TDC and a spike is observed with the combustion. It is also noticeable that the pressure declines with oscillatory behavior, when the piston moves away from TDC down to bottom. The oscillations occur due to chains of combustions. 3. Experimental setup In preliminary experiments, power and torque values are determined for maximum power and torque output conditions. In cylinder pressure measurements were recorded with using Kistler 6011 pressure transducer, Kistler 5011 type charge amplifier and LeCroy brand digital oscilloscope. Injection, pressure and incremental encoder signals recorded simultaneously with 0, 1 °CA intervals. The experimental setup is depicted in Fig. 3. 3.1. Experiment procedure Experiments are conducted based on procedure explained below:
Fig. 6. Cylinder pressure variations at 3000 rpm (injection advance 20 BTDC, pressure 1400 bar).
(4) Torque, speed and pressure of the cylinder are recorded. Pressure is observed to determine start of knocking. Number and duration of the injections are used to compute the amount of the fuel consumed. As it is noted in the Figs. 4 and 5, output torque (Md), energy (Ne) is increased even though specific fuel consumption (be) decreased with the LPG addition. The thermal efficiency of the engine (ge) increased. It is also obvious that the quality of the combustion is increased with electronic injection. The test results are analyzed and it was found that, an increase on performance was observed with the LPG addition. In general, we obtained maximum power for all the fuels at a spray angel of 20 CA before TDC. When the diesel injection pressure set to 1400 bar, 7.11 kW of power was obtained at 3000 rpm. At the same engine speed and Injection pressure conditions, diesel + 10% LPG showed 7.35 kW, diesel + 20% LPG and diesel + 25% LPG showed 7.70 kW and 7.81 kW respectively. However, reducing the injection advance before the TDC to 17 CA, caused a decrease in the value maximum power.
(1) Common-rail pressure and advance angle are set. (2) A speed value is determined and engine speed controller is set to operate engine at constant speed. (3) Engine is loaded with DC-motor and until the speed is decreasing. This point is the operating condition where engine can generate its maximum torque level for that speed. If load is increased, speed of the engine decreases even fuel consumption increases. Torque 26 25
Nm
24 23 22 21 20
DiESEL
DiESEL+10%LPG
DiESEL+%20%LPG
Advance 20
22,61
23,4
24,53
DiESEL+%25%LPG 24,88
Advance17
21,73
23
24,4
24,34
Fig. 5. Torque curves of diesel and dual operations.
Fig. 7. Cylinder pressure variations at 3000 rpm (injection advance 17 BTDC pressure 1400 bar).
278
A.T. Ergenç, D.Özde Koca / Fuel 130 (2014) 273–278
Fig. 6 compares cylinder pressures during the combustion at the highest power point for varying rates of LPG addition. It can be seen from that, the maximum cylinder pressure increases as LPG supply rate increases. This is due to earlier onset of combustion [26]. The maximum cylinder pressure raises around 5 bars with the LPG addition. However, the knocking (oscillate about the mean value) increased with the addition of LPG as result of higher burning velocity [16,26]. Fig. 7 compares cylinder pressures during the combustion at the highest power point for varying rates of LPG addition at a later diesel injection. At this test point, the engine control unit retards injection timing of the diesel fuel. It can be seen from the figure, the peak cylinder pressure values decreased with the late injection [1,26,27] The maximum cylinder pressure raises around 2 bars with the LPG addition.
4. Conclusion In this study, an experiment test bed is designed and constructed to determine optimum operation conditions for alternative fuels. In this bed, the duration, number of the phases, timing, number of the injectors and pressure of the injection are controlled. The aim is to determine the effects of controlled parameters on performance of the engine. A commercially available diesel engine is modified and converted into electronically controlled diesel engine with common-rail injection system and port fuel LPG injection system. The new injection systems are calibrated and preliminary experiments are conducted to test the controller. This new alternative fuel test bed has capabilities of testing the effects of several parameters as mention throughout the text. A very important fact about the experimental setup is that a PLC is utilized as ECU. A PLC is an unorthodox solution for engine control systems. Nevertheless, it is an economical resolution for a single cylinder engine based test bed. Besides, establishing algorithms and debugging of program codes are easier compared to a commonly used microcontroller based developing boards. It has advantage of observing the algorithm online while the controller is running. It is also shown that an electronic injection system and dual fuel operations increases the quality of the combustion in the engine which let us to compare alternative fuels (single or dual) in a more efficient way. In addition, the LPG sellers are studying on the performance of the compression ignition engine using diesel + LPG or diesel + LNG (liquefied natural gas) fuels. Starting from this point, to utilize LPG or hydrogen systems as dual fuel on the engine to increase the capabilities of the test bed.
Acknowledgment The test bed system equipments were financially supported by Yıldız Technical University, Scientific Research Projects Department.
References [1] Lata DB, Ashok Misra, Medhekar S. Investigations on the combustion parameters of a dual fuel diesel engine with hydrogen and LPG as secondary fuels. Inter J Hydrogen Energy 2011;36:13808–19. [2] Saleh HE. Effect of variation in LPG composition on emissions and performance in a dual fuel diesel engine. Fuel 2008;87:3031–9. [3] Elnajjar E, Hamdan MO, Selim MYE. Experimental investigation of dual engine performance using variable LPG composition fuel. Renew Energy 2013;56:110–6. [4] Abd Alla GH, Soliman HA, Badr QA, Abd Rabbo MF. Effect of injection timing on the performance of a dual fuel engine. En. Con. Man. 2002;43:269–77. [5] Qi DH, Bian YZH, MA ZHY, Zhang CHH, Liu SHQ. Combustion and exhaust emission characteristics of compression ignition engine using liquified petroleum gas–diesel blended fuel. En. Con. Man. 2007;48:500–9. [6] Homoyer C, Choi, Kim JH. Effects of different LPG fuel systems on performances of variable compression ratio single cylinder engine. ASME Int Combust Engine Div 2002;39:369–75. [7] Budzianowski WM, Miller R. Towards improvements in thermal efficiency and reduced harmful emissions of combustion processes by using recirculation of heat and mass: a review. Recent Patents Mech Eng 2009;2:228–39. [8] Xu J, Zhang X, Liu J, Fan L. Experimental study of a single cylinder engine fueled with natural gas-hydrogen mixtutes. Int J Hydrogen Energy 2010;35:2909–14. [9] Yoong APF, Watkins AP. Study of liquifed petroleum gas (LPG) spray modeling, Thermo Fluids, Division, Department of Mechanical Aerospace & Manufacturing Engineering, UMIST, Mancester, M60 1QD. ILASS- Europe, Zurich: UK; 2001. [10] Miller JNK, Nagarajan G, Renganarayan S, Experimental studies on homegeneous charge CI engine fueled with LPG using DEE as an ignition enhancer. Renew Energy. 2007:32;1581–93. [11] Poonia MP, Ramesh A, Gaur RR, Experimental investigation of the factors affecting THA performence of a LPG-diesel dual fuel engine. SAE paper 991123;57–65. [12] Ganesan S, Ramesh A. Experimental investigations of a LPG-diesel dual fuel engine. J THA Inst Eng 2002;83:105–11. _ Içten _ Yanmalı Motorlar, Eg˘itim Yayınları ASß. 1988. [13] Yavasßlıol I, _ [14] Denso Corporation, Opel 4EE2 tipi motor için Commonrail sistemi, Istanbul, 2003. [15] Desantes JM, Benajes J, Molina S, Gonzalez CA. The modification of the fuel injection rate in heavy-duty diesel engines Part 1: Effects on engine performance and emissions. Appl Therm Eng 2004:2701–14. [16] Heywood JB. Internal combustion engine fundamentals. Newyork: McGrawHill; 1988. [17] Hideyuki Ogawa, Noburo Miyamoto, Chenyu Li, Atsushi Sakai, Improvements of diesel combustion and emissions with two-stage fuel injection at different piston positions, SAE paper 2000;01–1180. [18] Ghaffarpour M, Baranescu R, NOx reduction using injection rate shaping and intercooling in diesel engines. SAE paper 960845. [19] Guzella L, Amstutz. Control of diesel engines. IEEE Contr Syst Mag 1998;5:53–71. [20] Reddy N, Ramesh A. Parametric studies for improving the performance of a Jatropha oil-fuelled compression ignition engine. Elsevier Renew Energy 2006;31:1994–2016. [21] Ergenç Alp Tekin, Ergenç Ali Fuat. A multi-purpose test-bed design for alternative diesel fuels transactions of the institute of measurement and control 2012;34:91–104. [22] Siemens Simatic S7–200 Programmable controller system manual, 2005. _ Ayhaner M, Dicle H. The characteristic differences in [23] Ergenc A, Yavasßlıol I, exhaust emissions, and fuel consumption analysis of unleaded gasolines produced by different oil companies in Turkish market. IJEP 2005;23:460–72. [24] Taglialatela F, Lavorgna M, Mancaruso E, Vaglieco BM. Determination of combustion parameters using engine crankshaft speed. MSSP 2013;38:628–33. [25] Karagiorgis S, Glover K, Collings N. Control challenges in automotive engine managment. EJC 2007;13:92–104. [26] Goldsworthy L. Combustion behaivor of a heavy duty common rail marine diesel engine fumigated with propane. ETFS 2012;42:93–106. [27] Lata DB, Misra Ashok. Theoretical and experimental investigations on the performance of dual fuel diesel engine with hydrogen and LPG as secondary fuels. Hydrogen Energy 2010;35:11918–31.
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
PLC controlled single cylinder diesel-LPG engine Alp Tekin Ergenç ⇑, Deniz Özde Koca Yildiz Tecnical University, Mechanical Engineering Department, IC Engines Laboratory, Turkey
h i g h l i g h t s Electronic injection system increases the quality of the combustion. We controlled all injectors by Programmable Logic Controller. A PLC is an unorthodox solution for engine control systems. The maximum cylinder pressure raises with the LPG addition. Reducing the injection advance before the TDC caused lower maximum power.
a r t i c l e
i n f o
Article history: Received 10 December 2013 Received in revised form 3 April 2014 Accepted 6 April 2014 Available online 24 April 2014 Keywords: Diesel engine LPG Injection Advance PLC
a b s t r a c t The main purpose of this work is to convert the mechanical injection system of a single cylinder diesel engine to an electronically controlled dual-fuel system. The new system consist two different injectors. First injector supplies the LPG (liquefied petroleum gas) , the other one supplies the diesel. LPG is supplied via a port fuel injection system located in the intake port of the engine and the diesel injected directly into the combustion chamber before top dead center (TDC). All injectors were controlled by Programmable Logic Controller (PLC). After the adaptation and tests, the single cylinder Lombardini LDA 450 type diesel engine was modified to a high pressured PLC controlled dual-fuel research engine. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Environmental concerns and depletion in petroleum resources have forced researchers to concentrate on finding alternatives to conventional petroleum fuels. A lot of experimental efforts are focused on simultaneous achievement of high energy efficiency and reduction of harmful emissions [7]. The emission problem divided into two parts. The first is the engine and the old car population; the second is the fuel. Due to developments in engine technology, the emission pollutants levels are high because of the fuel specifications. According to the new regulations the fuel specifications are more important for the vehicles [23]. At this point, the use of gaseous fuels in I.C. engines has long been considered as a possible method for reducing emissions while maintaining engine performance and efficiency [8]. LPG is considered, to be one of the most proficient alternative fuels not only as a replacement for petroleum fuel but also as a basis of reducing NOx, soot and particulate matter. LPG has a high octane rating and hence ⇑ Corresponding author. Tel.: +90 2123832835; fax: +90 2122616659. E-mail address: [email protected] (A.T. Ergenç). http://dx.doi.org/10.1016/j.fuel.2014.04.016 0016-2361/Ó 2014 Elsevier Ltd. All rights reserved.
well appropriate for S.I. engine. But when LPG is burnt in the usual diesel engine there is a difficulty in self-ignition because of its lower cetane number [10]. Nowadays, LPG becomes more attractive at our country, because of environmental benefits in terms of emissions and it is cheaper unit price. In general, SI (spark ignition) engine powered old cars fuel system changed into dual fuel (LPG/Gasoline) system. Recent years, due to the higher petrol prices and taxes, the unit price of gasoline and diesel rises dramatically. High diesel fuel price, have forced the issue of the use of LPG at diesel engine. Since the early 1930’s, there is a fluctuating interest in the research of compression engines operating on dual fuels. Recently, dual fuel engines are receiving more interest from many scientists due to many reasons including the national concerns of the liquid fuels limited resources, the environmental issues and the need to use a reliable, durable and efficient engine [3]. The dual fuel engines studies focuses on utilizing the gaseous fuels like natural gas, hydrogen and LPG as primary fuel in compression engines, due to the higher ignition temperature of this fuels. This primary fuels increases the mixture temperature [4]. Furthermore, because of the higher octane number of the gaseous
274
A.T. Ergenç, D.Özde Koca / Fuel 130 (2014) 273–278
fuels, it can be used in conventional high compression engine with minor modifications, with comparable efficiencies to diesel fuel [3] According to Yoong and Watkins, [9] a higher thermal efficiency and therefore, improved fuel economy can be obtained from internal combustion engines running on LPG as opposed to unleaded gasoline. This is because LPG has a higher octane number, typically 112 Research Octane Number for pure propane, which prevents the occurrence of detonation at high engine compression ratio [5]. Homoyer et al. [6] states that there is a penalty in power output when using LPG compared to gasoline due to the displacement of some of the inspired air by the fuel gas whose volume is much greater than that of its elated liquid. In dual fuel compressed ignition engines operating with LPG as primary fuel and a pilot amount of diesel fuel as an ignition source, the LPG is induced along with the intake air and is compressed like in a conventional diesel Engine. The mixture of air and LPG does not auto-ignite due to its high auto-ignition temperature. A Small amount of diesel fuel is injected near the end of the compression stroke to ignite the gaseous mixture. Poonia et al. [11] performed experiments on LPG-diesel dual fuel engine at various intake temperature and pilot quantities. It was found that by increase in the concentration of the gaseous primary fuel, ignition delay increases considerably. At higher load condition, the combustion of the gaseous fuel takes place by flame propagation after ignition of pilot fuel. Ganesan and Ramesh [12] used LPG as the primary fuel and diesel as pilot fuel. The brake thermal efficiency was increased from 35% in the diesel mode to 37% in dual fuel mode at full load condition due to rise in the combustion rate. However, at lower load condition and with high diesel substitution, brake thermal efficiency reduces and hydrocarbons and CO levels increase. It is also noted that NOx levels reduce in the dual fuel mode up to 60% of full load condition. The smoke emission reduces from 1.3 Bosch Smoke Units (BSU) to 0.5 (BSU) with dual fuel mode at full load. The ignition delay period increases by 2 °CA (crank angle) and the peak pressure decreases under light load and high diesel substitutions conditions. Saleh [2] studied the effects of LPG compositions on the exhaust emissions of the dual fuel compression engine under different engine conditions. This study reported that LPG with 70% propane blend is showing a similar performance compared to the conventional diesel engine. For the 70% propane blend, NOx and SO2 emission decreased by 27–69% meanwhile, the CO emission decreased by 15.7% compared to the conventional diesel engine. A high-quality formation for combustion is achieved by mixing of pulverized fuel drops and the air inside the cylinder [13]. In this matter, injection parameters such as timing and period of injection, injection pressure and number of the injection beams affect quality of combustion and mixture formation. At this point, injection system has an important role on mixture formation. Injection timing and period determines the beginning of the combustion in terms of crankshaft angle. Commercial single cylinder engines are produced with mechanical fuel injection systems, which have predetermined parameters. Thus the effects of different operational parameters such as advance angle, injection pressure, and duration and phase numbers cannot be tested. In a test engine, injectors should be controlled depending on the operational parameters of the engine (speed, gas position, etc.). In alternative fuel studies, the injection system parameters like pressure, injection advance, and injection character must be controllable. In general, single cylinder diesel test engines have mechanical unit pump systems and this system have no changeable parameters. Utilizing common-rail injection instead of mechanical injection pump can control timing and period. Common-rail mechanisms provide us to employ efficient and flexible control schemes on the injection system.
Application of high-pressure injection systems increases amount of fuel injection per crankshaft angle and also shortens the ignition delay. Naturally this delay has a minimum value that cannot be breached. The amount of the fuel injected into cylinder increases with the pressure till the ignition starts and this leads to higher levels of NOx and noise. In order to compensate these problems pre-injection technique is utilized. NOx and noise levels diminish with this method [14–18]. In addition, high-pressure injection improves specific fuel consumption and particle emission levels [19,20]. As a summary, in a test engine advance angle, duration and number of injections are the parameters subject to be adjusted to discover best blending ratios of alternative fuels. In addition, a measurement system is vital to measure torque output, speed, temperature, airflow rate, combustion pressure and emissions. The data collected from the system associated with control parameters and corresponding measurements can be used for system identification of the test engine and therefore; optimal operational region would be determined. In dual-fuel operation, LPG fuel injected with a system located to the intake port of the DI (direct injection) diesel engine and diesel fuel injected directly into the combustion chamber with an electromagnetic injector before top dead center. All injectors were controlled by Programmable Logic Controller. In dual fuel mode, with gas mixed into the air intake while liquid diesel is injected as normal, but a reduced rate [26]. 2. Engine management The test engine system for alternative fuels consists of three main parts. First part is the engine and its controller. Second part is the fuel system including common-rail pressure line and low pressure fuel line (dual fuel). Finally, the third part is the measurement system that includes all the sensors and transducers, which provides feedback from all the operational quantities listed above. A Single cylinder diesel engine is coupled with a DC motor over a belt pulley mechanism with a ratio of 1:2. A two quadrant driver is attached to DC motor. In the first quadrant, it operates as a starter motor for the engine and in the second one, as a generator to load the engine. 2.1. Engine Controller Unit (ECU) Electronic engine controls based on real time diagnosis of combustion process can significantly help in complying with the exhaust emission regulations and fuel consumption. Information on the combustion efficiency may provide a strong tool regarding engine operation and may be profitably used for closed-loop electronic engine controls [24,25]. In an electronically controlled engine system a micro-controller based controller is necessary to collect data and generate necessary signals to drive the injectors (LPG and diesel) in real-time. Programmable Logic Controllers (PLC), which particularly developed for industrial automation, can be utilized for controlling single cylinder engine. PLC have real-time operating systems, timers and counters crucial for real-time control systems. Another advantage of is that PLCs are relatively economical resolution for control applications. PLC, as an ECU, collects data from sensors such as crankshaft encoder, pressure and temperature transducers, then generates driving signals of the injectors. Siemens S7-200 series CPU224 PLC is suitable with its 14 digital inputs and 10 digital outputs. An analog module is attached to the PLC for analog data acquisition [22]. In the PLC used as the controller, there are precision timers for injection timing, high-speed counters for counting incremental
275
A.T. Ergenç, D.Özde Koca / Fuel 130 (2014) 273–278
encoder pulses to achieve crankshaft position and high-speed pulse generators for injection signals. A TD200 HM interface is utilized for entering the position of virtual gas pedal position, injection advance angle values and displaying user data such as rpm, common-rail pressure value. Addition to displaying data, HM interface is used to switch operation modes between constant speed control mode and injector calibration mode. An IVO brand incremental encoder, which has 360 lines/rev, is used to assess the position of the crankshaft. Its zero position is set to top dead center of piston. TDC is determined by visual measurement of the piston after cylinder head is opened. It is marked when the piston altered its direction during its reciprocating motion when both valves (intake and exhaust) are closed. It is essential to detect exact position of the crankshaft in order to provide right injection advance angle for the engine. A single degree offset from the actual crankshaft angle would change the characteristics of the combustion in the engine drastically. Incremental encoder is connected to two high-speed counters of the PLC to trigger event-based interrupt subroutines in order to generate two different fuel injections with two different injectors. Event-based interrupt subroutines run when counters reach to preset values. In the interrupt, pulse width modulated injection signals are generated from the high-speed output of the PLC. In the time-based interrupt cycle of the PLC, encoder signals are used to compute the speed of the engine by the number of the pulses per sampling time.
2.2. Dual fuel system Electronically controlled fuel injection system should provide same performance from the engine, so the duration of injection of the electromagnetic injector is subject to be correlated with the SFC. The step after determination of SFC for mechanical injector is to calibrate the electromagnetic injector for the same operation regime. Shortly, it is necessary to determine the amount of fuel injected per time when injector is open. Naturally, the amount is function of not only injection duration but also common-rail pressure. After the mechanical tests, the diesel engine was modified for dual fuel application. Common-rail fuel injection system (900– 1600 bar of injection pressure) and LPG injection system were adapted to the test engine. The LPG injector positioned directly to the upstream of intake valve. Specifications of the test engine are listed in the Table 1. The test bed is illustrated in Fig. 1. The pressure of the common-rail (diesel) is generated by a radial pressure pump with three pistons. In the test bed, the pump is driven by a 3HP three-phase induction motor. The diesel fuel supplied from the fuel tank. The LPG fuel system is more basic than the common-rail. An ordinary LPG tank, LPG filter, regulator, and a rail were used to supply the LPG to the injector. The pressure in common-rail is controlled for the reference values between 200 and 1600 bars. These values are selected to test injector behavior and also variation of combustion quality depending on the pressure. In radial pressure pumps, output pressure is
Table 1 Technical specifications of LDA 450. Total displacement Number of cylinders Injection timing (electronically) Bore Stroke Max. torque at 2200 rpm Max. power at 3000 rpm
454 cm3 Single Changeable – BTDC 85 mm 80 mm 28.5 Nm 7.5 kW
High pressure Diesel pump Diesel injector
LPG injector
DC Motor
Fig. 1. LPG ınjected PLC controlled single cylinder diesel engine test bed.
controlled via PWM signal, which switches the plungers on and off. A pressure transducer is utilized for feedback. 2.3. Injector calibration The common rail injector’s calibration experiments are conducted for 900–1600 bars by 100 bars increments without combustion. In the preliminary experiments, substantial variations of injection characteristics are recorded depending on fuel temperature. In order to avoid these variations, a cooler is utilized to keep the temperature of the fuel below 40 C. Sartorius brand precision scale is used to measure the weight of the fuel injected for certain amount of injection duration. For common rail experiment, injector is triggered 1000 times into a container and the weight of the diesel is measured. The LPG injector’s calibration experiments are conducted for standard pressure at different opening durations. The injector is triggered several times .The number of LPG injections is counted at different opening durations to spend 10 g of LPG Fuel. After the calibration, the relation between the power output and injection duration is determined. The next step is to establish control of the engine with a microcontroller-based system. 2.4. Engine control algorithm It is well known that in diesel engines, combustion occurs when fuel–air mixture is compressed tightly. The main factors in this operation are the quality of the fuel–air mixture and compression ratio. Due to mechanical constraints compression ratios is kept constant. On the other hand, mixture formation is a parameter that we can manipulate. In the conventional diesel engines, which have no turbo charger, there are four parameters that can be controlled; advance angle, amount of injected fuel, pressure of the injection and the number of the injection phases. The controller of the test unit should be able manipulate all these parameters. As mentioned earlier, a PLC is an economic resolution as a controller. It has all essential units for creating an ECU. It has analog inputs to read feedback, high-speed counters to detect encoder outputs for measuring crank-shaft angle, event-based interrupt capability for injection algorithms, and high-speed digital outputs for generating PWM (Pulse width modulation) signals for pressure control and PTO (Pulse train output)) signals for injector control. It also has real-time clock, which is essential for real-time control systems [21,22]. The flowchart of the control algorithm is displayed in Fig. 2a. Injection is started at advance angle from TDC and continued for
276
A.T. Ergenç, D.Özde Koca / Fuel 130 (2014) 273–278
Fig. 2. (a) Diesel engine control algorithm and (b) control and feedback signals.
Fig. 3. Experimental set-up.
A.T. Ergenç, D.Özde Koca / Fuel 130 (2014) 273–278
277
Power
8 7,8 7,6
kW
7,4 7,2 7 6,8 6,6 6,4 6,2
DİESEL+10%LPG
DİESEL+%20%LPG
DİESEL+%25%LPG
Advance 20
DİESEL 7,11
7,35
7,7
7,81
Advance17
6,82
7,22
7,66
7,64
Fig. 4. Power curves of diesel and dual operations.
an amount of time (injection duration). Both of these values are controlled. In Fig. 2b, encoder signal for bottom dead center (BDC), injection signals and pressure in the cylinder is displayed. The encoder signal from BDC is used, because the high-speed counter is reset at TDC. As it is visible, the inner pressure of the cylinder increases when the piston reaches to TDC and a spike is observed with the combustion. It is also noticeable that the pressure declines with oscillatory behavior, when the piston moves away from TDC down to bottom. The oscillations occur due to chains of combustions. 3. Experimental setup In preliminary experiments, power and torque values are determined for maximum power and torque output conditions. In cylinder pressure measurements were recorded with using Kistler 6011 pressure transducer, Kistler 5011 type charge amplifier and LeCroy brand digital oscilloscope. Injection, pressure and incremental encoder signals recorded simultaneously with 0, 1 °CA intervals. The experimental setup is depicted in Fig. 3. 3.1. Experiment procedure Experiments are conducted based on procedure explained below:
Fig. 6. Cylinder pressure variations at 3000 rpm (injection advance 20 BTDC, pressure 1400 bar).
(4) Torque, speed and pressure of the cylinder are recorded. Pressure is observed to determine start of knocking. Number and duration of the injections are used to compute the amount of the fuel consumed. As it is noted in the Figs. 4 and 5, output torque (Md), energy (Ne) is increased even though specific fuel consumption (be) decreased with the LPG addition. The thermal efficiency of the engine (ge) increased. It is also obvious that the quality of the combustion is increased with electronic injection. The test results are analyzed and it was found that, an increase on performance was observed with the LPG addition. In general, we obtained maximum power for all the fuels at a spray angel of 20 CA before TDC. When the diesel injection pressure set to 1400 bar, 7.11 kW of power was obtained at 3000 rpm. At the same engine speed and Injection pressure conditions, diesel + 10% LPG showed 7.35 kW, diesel + 20% LPG and diesel + 25% LPG showed 7.70 kW and 7.81 kW respectively. However, reducing the injection advance before the TDC to 17 CA, caused a decrease in the value maximum power.
(1) Common-rail pressure and advance angle are set. (2) A speed value is determined and engine speed controller is set to operate engine at constant speed. (3) Engine is loaded with DC-motor and until the speed is decreasing. This point is the operating condition where engine can generate its maximum torque level for that speed. If load is increased, speed of the engine decreases even fuel consumption increases. Torque 26 25
Nm
24 23 22 21 20
DiESEL
DiESEL+10%LPG
DiESEL+%20%LPG
Advance 20
22,61
23,4
24,53
DiESEL+%25%LPG 24,88
Advance17
21,73
23
24,4
24,34
Fig. 5. Torque curves of diesel and dual operations.
Fig. 7. Cylinder pressure variations at 3000 rpm (injection advance 17 BTDC pressure 1400 bar).
278
A.T. Ergenç, D.Özde Koca / Fuel 130 (2014) 273–278
Fig. 6 compares cylinder pressures during the combustion at the highest power point for varying rates of LPG addition. It can be seen from that, the maximum cylinder pressure increases as LPG supply rate increases. This is due to earlier onset of combustion [26]. The maximum cylinder pressure raises around 5 bars with the LPG addition. However, the knocking (oscillate about the mean value) increased with the addition of LPG as result of higher burning velocity [16,26]. Fig. 7 compares cylinder pressures during the combustion at the highest power point for varying rates of LPG addition at a later diesel injection. At this test point, the engine control unit retards injection timing of the diesel fuel. It can be seen from the figure, the peak cylinder pressure values decreased with the late injection [1,26,27] The maximum cylinder pressure raises around 2 bars with the LPG addition.
4. Conclusion In this study, an experiment test bed is designed and constructed to determine optimum operation conditions for alternative fuels. In this bed, the duration, number of the phases, timing, number of the injectors and pressure of the injection are controlled. The aim is to determine the effects of controlled parameters on performance of the engine. A commercially available diesel engine is modified and converted into electronically controlled diesel engine with common-rail injection system and port fuel LPG injection system. The new injection systems are calibrated and preliminary experiments are conducted to test the controller. This new alternative fuel test bed has capabilities of testing the effects of several parameters as mention throughout the text. A very important fact about the experimental setup is that a PLC is utilized as ECU. A PLC is an unorthodox solution for engine control systems. Nevertheless, it is an economical resolution for a single cylinder engine based test bed. Besides, establishing algorithms and debugging of program codes are easier compared to a commonly used microcontroller based developing boards. It has advantage of observing the algorithm online while the controller is running. It is also shown that an electronic injection system and dual fuel operations increases the quality of the combustion in the engine which let us to compare alternative fuels (single or dual) in a more efficient way. In addition, the LPG sellers are studying on the performance of the compression ignition engine using diesel + LPG or diesel + LNG (liquefied natural gas) fuels. Starting from this point, to utilize LPG or hydrogen systems as dual fuel on the engine to increase the capabilities of the test bed.
Acknowledgment The test bed system equipments were financially supported by Yıldız Technical University, Scientific Research Projects Department.
References [1] Lata DB, Ashok Misra, Medhekar S. Investigations on the combustion parameters of a dual fuel diesel engine with hydrogen and LPG as secondary fuels. Inter J Hydrogen Energy 2011;36:13808–19. [2] Saleh HE. Effect of variation in LPG composition on emissions and performance in a dual fuel diesel engine. Fuel 2008;87:3031–9. [3] Elnajjar E, Hamdan MO, Selim MYE. Experimental investigation of dual engine performance using variable LPG composition fuel. Renew Energy 2013;56:110–6. [4] Abd Alla GH, Soliman HA, Badr QA, Abd Rabbo MF. Effect of injection timing on the performance of a dual fuel engine. En. Con. Man. 2002;43:269–77. [5] Qi DH, Bian YZH, MA ZHY, Zhang CHH, Liu SHQ. Combustion and exhaust emission characteristics of compression ignition engine using liquified petroleum gas–diesel blended fuel. En. Con. Man. 2007;48:500–9. [6] Homoyer C, Choi, Kim JH. Effects of different LPG fuel systems on performances of variable compression ratio single cylinder engine. ASME Int Combust Engine Div 2002;39:369–75. [7] Budzianowski WM, Miller R. Towards improvements in thermal efficiency and reduced harmful emissions of combustion processes by using recirculation of heat and mass: a review. Recent Patents Mech Eng 2009;2:228–39. [8] Xu J, Zhang X, Liu J, Fan L. Experimental study of a single cylinder engine fueled with natural gas-hydrogen mixtutes. Int J Hydrogen Energy 2010;35:2909–14. [9] Yoong APF, Watkins AP. Study of liquifed petroleum gas (LPG) spray modeling, Thermo Fluids, Division, Department of Mechanical Aerospace & Manufacturing Engineering, UMIST, Mancester, M60 1QD. ILASS- Europe, Zurich: UK; 2001. [10] Miller JNK, Nagarajan G, Renganarayan S, Experimental studies on homegeneous charge CI engine fueled with LPG using DEE as an ignition enhancer. Renew Energy. 2007:32;1581–93. [11] Poonia MP, Ramesh A, Gaur RR, Experimental investigation of the factors affecting THA performence of a LPG-diesel dual fuel engine. SAE paper 991123;57–65. [12] Ganesan S, Ramesh A. Experimental investigations of a LPG-diesel dual fuel engine. J THA Inst Eng 2002;83:105–11. _ Içten _ Yanmalı Motorlar, Eg˘itim Yayınları ASß. 1988. [13] Yavasßlıol I, _ [14] Denso Corporation, Opel 4EE2 tipi motor için Commonrail sistemi, Istanbul, 2003. [15] Desantes JM, Benajes J, Molina S, Gonzalez CA. The modification of the fuel injection rate in heavy-duty diesel engines Part 1: Effects on engine performance and emissions. Appl Therm Eng 2004:2701–14. [16] Heywood JB. Internal combustion engine fundamentals. Newyork: McGrawHill; 1988. [17] Hideyuki Ogawa, Noburo Miyamoto, Chenyu Li, Atsushi Sakai, Improvements of diesel combustion and emissions with two-stage fuel injection at different piston positions, SAE paper 2000;01–1180. [18] Ghaffarpour M, Baranescu R, NOx reduction using injection rate shaping and intercooling in diesel engines. SAE paper 960845. [19] Guzella L, Amstutz. Control of diesel engines. IEEE Contr Syst Mag 1998;5:53–71. [20] Reddy N, Ramesh A. Parametric studies for improving the performance of a Jatropha oil-fuelled compression ignition engine. Elsevier Renew Energy 2006;31:1994–2016. [21] Ergenç Alp Tekin, Ergenç Ali Fuat. A multi-purpose test-bed design for alternative diesel fuels transactions of the institute of measurement and control 2012;34:91–104. [22] Siemens Simatic S7–200 Programmable controller system manual, 2005. _ Ayhaner M, Dicle H. The characteristic differences in [23] Ergenc A, Yavasßlıol I, exhaust emissions, and fuel consumption analysis of unleaded gasolines produced by different oil companies in Turkish market. IJEP 2005;23:460–72. [24] Taglialatela F, Lavorgna M, Mancaruso E, Vaglieco BM. Determination of combustion parameters using engine crankshaft speed. MSSP 2013;38:628–33. [25] Karagiorgis S, Glover K, Collings N. Control challenges in automotive engine managment. EJC 2007;13:92–104. [26] Goldsworthy L. Combustion behaivor of a heavy duty common rail marine diesel engine fumigated with propane. ETFS 2012;42:93–106. [27] Lata DB, Misra Ashok. Theoretical and experimental investigations on the performance of dual fuel diesel engine with hydrogen and LPG as secondary fuels. Hydrogen Energy 2010;35:11918–31.