- Email: [email protected]
Experimental study on engine combustion and particle size distributions fueled with Jet A-1
Fuel xxx (xxxx) xxxx
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Full Length Article
Experimental study on engine combustion and particle size distributions fueled with Jet A-1 ⁎
⁎
Wenbin Yua, Yichen Zonga, Qinjie Lina, Kunlin Taya, Feiyang Zhaoa, , Wenming Yanga, , Markus Kraftb,c a
Department of Mechanical Engineering, National University of Singapore, Singapore School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore c Department of Chemical Engineering and Biotechnology, University of Cambridge, United Kingdom b
A R T I C LE I N FO
A B S T R A C T
Keywords: Jet A-1 Particle mode Particle size distribution Particle number concentration Particulate matter
In this study, a comprehensive investigation of combustion and emission characteristics of Jet A-1 applied in diesel engine was experimentally conducted. Analysis is emphasized on engine performance and soot particle emission both in size and number concentrations when fueled with Jet A-1, compared with traditional diesel fuel. It is concluded that compared with diesel combustion, the combustion phase is obviously retarded when fueled with Jet A-1. The premixed combustion fraction with Jet A-1 is increased and the peak of premixed heat release of Jet A-1 is higher compared with diesel combustion under different injection pressures and different engine loads. Fuel economy with Jet A-1 is significantly improved compared with diesel, which is because of higher low heating value of Jet A-1 as well as more intensive heat release near top dead center (TDC). Jet A-1 and diesel show similar trends in particle size distribution along with the changes of engine loads. Under the low engine load, the particle size distribution is basically dominated by nucleation mode, meanwhile higher concentration of nucleation particles is observed when fueled with Jet A-1 compared to diesel. As the engine load increases, the accumulation particles are increased while the nucleation particles are in turn decreased. When the engine is running under high engine load, the particle size distribution is dominated by accumulation mode. Based on these findings, the potential to improve fuel economy and reduce particulate matter (PM) emissions by using Jet A-1 in a diesel engine was therefore proposed.
1. Introduction Jet fuel is becoming more and more important in industrial and military applications. It is used not only for the rocket engines [1] and gas turbine engines [2] but also for diesel engines [3]. One of the reasons of the usage of jet fuel in diesel engines is the Single Fuel Concept (SFC) introduced by the United Sates army military, which could help to improve and simplify the fuel supply chain during both wartime and peacetime [4]. The other reason is that the aviation jet fuel is cheaper than diesel. As reported in 2017, the price of aviation jet fuel is US$1.558/gallon while the ultra-low-sulphur diesel is US$1.620/ gallon [5]. Diesel engines are widely used for both civilian and military applications due to the high thermal efficiency as well as the high torque relative to the gasoline engine [6]. However, compared with gasoline engine, the shortcoming of the diesel engine is also more obvious in the aspects of exhaust emissions, especially the PM emissions [6]. Over
⁎
decades, strict emissions standards [7] were implemented to regulate diesel engine emissions. The traditional diesel engines are developed specifically for diesel fuel, as such, the usage of other alternative fuels in diesel engines with different fuel properties such as jet fuel must be deeply investigated in case of adverse effects on engine emissions. A deep understanding of the jet fuel autoignition characteristics, jet fuel spray and spray-guided combustion are important for its successful usage in diesel engines. In the past years, lots of researchers investigated the autoignition characteristics using different equipment including shock tube, rapid compression machine (RCM), fuel ignition tester (FIT), ignition quality tester (IQT), constant volume combustion chamber (CVCC) and engines [8–13]. Various researchers had contributed significant studies on the constant volume spray and combustion of jet fuel, such as Pickett and Hoogterp [13], Lee and Bae [3], Park et al. [14], Jing et al. [15], Kang et al. [16], Song et al. [17] and the authors’ research group [18,19]. In recent years, lots of investigations on engine combustion and emissions fueled with jet fuel have been
Corresponding authors. E-mail addresses: [email protected] (F. Zhao), [email protected] (W. Yang).
https://doi.org/10.1016/j.fuel.2019.116747 Received 11 July 2019; Received in revised form 30 October 2019; Accepted 24 November 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Wenbin Yu, et al., Fuel, https://doi.org/10.1016/j.fuel.2019.116747
Fuel xxx (xxxx) xxxx
W. Yu, et al.
carried out. Lee et al. [3] reported that jet fuel combustion in a diesel engine had a longer ignition delay than diesel, which is primarily due to its lower CN. By using EGR along with optimized injection strategies, further optimization for both NOx and soot emissions from jet fuel combustion was proven to be possible without loss of efficiency [20]. The three most common used conventional jet fuels are Jet-A, Jet A1 and JP-8. Jet A is used only in the United State while Jet A-1 is used throughout the rest of the world [4]. The freezing point of Jet A is at −40 °C while that of Jet A-1 is at −47 °C [4]. Currently, although some engine experimental works fueled with jet fuel such as JP8 had been done, however, there are no researchers to do comprehensive and indepth investigations on PM emissions including particle size distribution and number concentration when fueled with Jet A-1 in diesel engines. In order to bridge this research gap, in this study, an engine experimental study fueled with Jet A-1 and diesel was conducted. A comprehensive investigation regarding the effect of engine parameters and fuel properties on engine performance, combustion process, particle size distribution and particle number concentration was done. Hence, the key factors that influence the particle emissions when fueled with Jet A-1 could be consequently figured out.
Table 1 Engine specifications. Brand
Yanmar
Bore × Stroke Displacement Compression Ratio Injection system Injection Pressure Rated output power
92 × 96 mm 0.638 L 17.7 Common rail 200 MPa Max. 7.8/2400 kW/rpm
current can be calibrated to adapt varied brands injectors from open market. It can also control common rail pressure, throttle valve, exhaust gas recirculation (EGR) valve, variable-geometry turbocharger (VGT), et al. Besides, the control system can be used to simulate a virtual engine to validate control strategies. A real-time combustion analysis, data acquisition and diagnosis system, which was embedded in the next-cycle control system, was used for the diagnosis of engines and engine relevant components such as all kinds of sensors and electronic control actuators. Same with the work done by Nargunde Jagdish et al. in 2010 [24], in this study, apparent heat release rate (AHRR) is calculated from incylinder pressure curve during the firing of the engine after subtracting the heat release rate during motoring under same cylinder wall temperature conditions. The motoring heat release rate trace was recorded by interrupting the fuel supply for a few numbers of cycles momentarily during the steady state condition. This was done in an effort to maintain the same cylinder wall temperature for both firing and motoring. The data acquisition software uses following formula to calculate the AHRR at any given crank angle degree [6].
2. Experimental procedures 2.1. Experimental setup The experimental study was conducted on a single-cylinder diesel engine and the schematic of experimental setup can be shown in Fig. 1. The single-cylinder research engine was provided by Yanmar Co., Ltd. while a common rail high pressure fuel injection system from Denso was equipped. Table 1 shows the specifications of the test engine. A next-cycle control system based on combustion analysis was developed in-house for engine control, which can also be seen in Fig. 1. Next-cycle control is the process of rapidly collecting cylinder pressure data and doing the post process for use in a control loop with enough time to adjust engine control parameters and command actuators for the next combustion cycle. With next-cycle control, certain combustion conditions such as crank angle for 50% heat release (CA50) can be targeted and accurately controlled between every cycle of the engine. Field-programmable gate array (FPGA) with the real-time computing hardware are used. This control system is flexible and extendable which can control both piezo and solenoid injectors. It can control injection timing, injection duration and multiple injections, while the injector
γ dp dQn dV 1 = p + V dt γ − 1 dt γ − 1 dt
(1)
Here ‘p’ is cylinder pressure; ‘V’ is swept volume, ‘γ’ is the ratio of specific heats and is assumed as a constant number of 1.4. The concentrations of CO2, CO, O2, NOx and HC in the exhaust gas were measured using a gas analyzer from AVL. The exhaust particle size distribution and number concentration were measured with a Differential Mobility Spectrometer 500 (DMS500) provided by Cambustion Ltd. As stated by Cambustion Ltd [21], the DMS500 uses a high voltage discharge to charge each particle proportional to its surface area. Charged particles are introduced into a classification section with a strong radial electrical field. This field causes particles to drift
Fig.1. Schematic diagrams of experimental setup. 2
Fuel xxx (xxxx) xxxx
W. Yu, et al.
through a sheath flow toward the electrometer detectors. Particles are detected at different distances down the column, depending upon their aerodynamic drag/charge ratio. Outputs from the 22 electrometers are processed in real-time at 10 Hz to provide a number/size spectrum for particles between 5 and 1000 nm.
Table 3 Fuel properties. Properties 3
Density at 15 °C (kg/m ) Viscosity at 40 °C (mm2/s) Cetane number Aromatics (vol%) Low Calorific value (MJ/Kg) Flash point (°C)
2.2. Particle size analysis Air pollution now is presenting a big challenge for the sustainable development of the entire world. It has been pointed out that long term exposure to ambient fine particulates (< 1000 nm) is associated with increased mortality and morbidity from diseases of pulmonary and cardiovascular [22]. Epidemiological investigations also revealed that ultrafine particles (< 100 nm) from soot emissions may have sever adverse health effects, considering their larger likelihood of penetration and higher surface area per unit volume to adsorb organic compounds [23]. In our present work, in order to do detailed analysis, the particle size distribution is separated into two regions including nucleation mode (2–50 nm) and accumulation mode (50–300 nm), which is the same with the previous investigation done in 2010 [24]. Such classification is useful for a deeper understanding of the effect of various engine parameters on PM emissions.
Diesel
804 1.13 [25] 42 18.8% [27] 43.2 38
831 3 [26] 52 35% [24] 42.7 55
the two injection pressures and test engine loads. This can also be revealed intuitively by the CA50 in comparison between Jet A-1 and diesel in Fig. 3. This phenomenon is mainly related with the lower cetane number of Jet A-1 (Jet A-1:42, diesel: 52) [20]. The AHRR curves also indicate that the fraction of premixed combustion by Jet A-1 is increased with higher peak compared to diesel combustion under test injection pressures and engine loads. This is mainly attributed to more accumulation of fuel in combustion chamber before ignition caused by the increased ignition delay when fueled with Jet A-1. Besides, another reason is that the Jet A-1 which has a lower viscosity than diesel (shown in Table 3) undergoes atomization more easily and therefore experiences a shorter penetration with a wider spray angle, which can be deduced from the authors’ previous spray study of Jet fuel [26,28,29]. As shown in Fig. 4, under low (30%) engine load, NOx emission from Jet A-1 combustion is about 10% higher than that from diesel combustion due to higher premixed combustion fraction of Jet A-1. However, based on the heat release traces comparison in Fig. 2 it can be seen that, both Jet A-1 and diesel combustion at middle (50%) and high (70%) engine loads are typically dominated by diffusion combustion, which present lower premixed combustion fraction than the low (30%) engine load. As such, NOx emission from Jet A-1 combustion is almost the same with that from diesel combustion at middle (50%) and high (70%) engine loads because the NOx emission here is mainly from diffusion combustion. Fig. 5 shows the HC emission comparison between Jet A-1 and diesel under different engine loads, injection timings and injection pressures. It should be noted that the final HC emissions are the result of the combined influence of many factors such as the spray, atomization, fuel properties, combustion temperature and fuelair equivalence ratio. In this study, the HC emission from Jet A-1 combustion is higher than diesel, as shown in Fig. 5. Firstly, the main reason is that a locally fuel-lean mixture with Jet A-1 was formed mainly due to the longer ignition and higher volatility [14]. In terms of the combustion regime, higher HC emission was obtained with premixed dominated combustion from the over-lean mixture by the longer mixing time. Similar result and explanation were also concluded by Park Y et al. [14]. Secondly, it also can be seen in Fig. 2 that in all cases the onset of heat release profile of Jet A-1 is retarded, but combustion ends at the same time. This indicates that Jet A-1 has shorter combustion duration leading to shorter time for fuel oxidation, which can also explain the phenomenon that the HC emission from Jet A-1 is higher than diesel. Table 4 shows that the indicated specific fuel consumption (ISFC) with different engine loads, injection timings and injection pressures. It can be seen that the fuel consumption is generally improved when fueled with Jet A-1. The largest improvement is 2.71% which is under 70% engine load, while the average improvement for all cases shown in Table 4 is around 1.84%. Firstly, the higher low heating value of Jet A-1 compared to diesel is one of the contributions to the better fuel economy. Secondly, the peak of the premixed heat release of Jet A-1 is higher and the premixed combustion fraction with Jet A-1 is increased compared with diesel combustion, leading to more concentrated heat release and higher local combustion temperature, which may help to improve the indicated thermal efficiency of the diesel engine combustion.
2.3. Experimental conditions In this study, the engine speed is fixed at 1400 rpm and three different engine loads of 30%, 50% and 70% were selected to represent low, middle and high engine loads to investigate the engine combustion process, exhaust gas and PM emissions characteristics of Jet A-1, comparing to traditional diesel fuel. The maximum output torque for this single-cylinder diesel engine at 1400 rpm is 40 Nm, so the absolute engine torque is 12, 20 and 28 Nm under three engine loads respectively. In the study, the experiment is conducted based on the torque which can be read by the dynamometer, this means, for a constant engine load, the injection amount may be different because of the application of different fuels and different injection pressures. In the experiment, the cycle change of the engine load varies within 5%. Besides, two injection pressures of 600, 800 bar and three start of injection timings (SOI) of −5, 0, 5 deg.ATDC were selected in the engine experiment. The experimental conditions and fuel properties can be seen in Tables 2 and 3 respectively. 3. Results and discussion 3.1. Combustion and gas emissions characteristics of Jet A-1 Fig. 2 indicates the in-cylinder pressure and AHRR for Jet A-1 and diesel under two injection pressures (600, 800 bar) and three engine loads (30%, 50%, 70%). The start of injection timing is fixed at 0 deg.ATDC. It is evident that the in-cylinder pressure increases and the heat release rate is becoming advanced with the increase of the injection pressure for both jet A-1 and diesel. This is because faster fuel spray, smaller droplet atomization and better fuel-air mixing can enhance the fuel premixed combustion under higher injection pressures. It can be seen in Fig. 2 that, compared with diesel combustion, the combustion phase is obviously retarded when fueled with Jet A-1 under Table 2 Experimental conditions. Speed Load Intake pressure Injection pressure Injection strategy Start of injection timing (SOI) Test fuels
Jet A-1
1400 rpm 30%, 50%, 70% Ambient pressure 600, 800 bar Single injection −5, 0, 5 deg.ATDC Jet A-1, diesel
3
Fuel xxx (xxxx) xxxx
W. Yu, et al.
Fig. 2. In-cylinder pressure and AHRR traces with different injection pressures under engine loads of (a) 30%, (b) 50% and (c) 70% (SOI: 0 deg.ATDC).
Fig. 3. CA50 with different engine loads and injection timings under injection pressures of (a) 600 bar and (b) 800 bar.
Fig. 4. NOx emissions with different engine loads and injection timings under injection pressures of (a) 600 bar and (b) 800 bar. 4
Fuel xxx (xxxx) xxxx
W. Yu, et al.
Fig. 5. HC emissions with different engine loads and injection timings under injection pressures of (a) 600 bar and (b) 800 bar.
load, which can be deduced from the lower in-cylinder pressures compared to higher engine loads as seen in Fig. 2, prefers the formation of the nucleation particles [30]. It should be noted that, compared with diesel, more nucleation mode particles can be observed when fueled with Jet A-1 under 30% load without significant variations for the different injection timings and injection pressures, as seen in Fig. 7. One of the reasons could be related with higher HC emission of Jet A-1 caused by more intensive premixed combustion [13,31]. In addition, due to lower carbon number of Jet A-1 than that of diesel, the Jet A-1 combustion more favours nucleation mode particles under the conditions of leaner combustion or lower temperature combustion [32]. Moreover, higher concentrations of nucleation mode particles from Jet A-1 combustion can also reflect the fact that the HC emission from Jet A-1 is higher than diesel under some certain conditions. Fig. 10 shows the particle number concentrations of different modes under different engine loads and injection pressures. It can be seen in Fig. 10(a), (a1), (b) and (b1) intuitively that under 30% engine load condition the particle number concentration of nucleation mode particles is much more than that of accumulation mode particles, which reveals that the particles under 30% engine load are dominated by nucleation mode without significant variations for different injection timings and injection pressures. When the engine is running under 50% load conditions, more injected fuel leads to an increase of local equivalence ratios. Besides, the combustion mode obviously transits from premixed dominated combustion to diffusion combustion along with higher combustion temperature, which promotes the nuclei-precursor particles formation process. Once more nuclei particles are available, the subsequent surface growth and coagulation processes are therefore enhanced [33]. The depiction here can help to explain that under 50% load condition, the nucleation mode particles are decreased compared with 30% engine load, while the accumulation mode particles are increased to some extent, as seen in Fig. 6. Accumulation mode particles in combustion are known to act as adsorption site for the gases responsible for the formation of the nucleation mode particles, which means as the accumulation mode particles increase, the gases that synthesizes nucleation mode particles are more likely to be adsorbed on the accumulation particles. This is also another reason for the reduction of the nucleation particles. Finally, it can be seen in Fig. 8 that in all cases the nucleation mode particles of Jet A-1 and diesel are at almost the same level as well as the accumulation mode particles. This can also be intuitively shown in Fig. 10 by the statistics of particle number concentrations of different particle modes: the nucleation mode particle number concentration of
Table 4 ISFC with different engine loads, injection timings and injection pressures. Engine load (%)
Injection pressure (bar)
SOI (deg.ATDC)
ISFCd (g/kWh)
ISFCJ (g/kWh)
(ISFCJ – ISFCd)/ ISFCd *100% (%)
30%
600
−5 0 5 −5 0 5 −5 0 5 −5 0 5 −5 0 5 −5 0 5
226.51 218.50 218.03 233.08 217.39 207.37 201.58 200.16 198.83 205.30 199.78 199.89 196.46 199.25 202.85 197.46 194.79 197.84
220.52 214.65 216.23 228.82 213.98 203.62 197.67 195.06 195.33 201.93 194.53 198.66 194.19 195.96 200.15 192.77 190.20 192.48
−2.64 −1.76 −0.83 −1.83 −1.57 −1.81 −1.94 −2.55 −1.76 −1.64 −2.63 −0.62 −1.16 −1.65 −1.33 −2.37 −2.36 −2.71
800
50%
600
800
70%
600
800
ISFCd and ISFCJ stand for ISFC of diesel and Jet A-1 respectively.
3.2. Particulate matter emission characteristics of Jet A-1 Fig. 6 shows the particle size distribution with different engine loads, indicating that Jet A-1 and diesel present similar trends in the particle size distribution along with the changes of engine loads: (1) Under the low engine load (30% load), the particle size distribution is mainly dominated by nucleation mode. (2) Under the middle engine load (50% load), the proportion of nucleation mode particles are decreased compared with 30% engine load. The nucleation mode and accumulation mode are almost at the same level. (3) Under the high engine load (70% load), the particle size distribution is typically dominated by accumulation mode. When the engine is running under 30% engine load condition, the less fuel injection leads the local equivalence ratios towards lean-conditions, significantly limiting the formation process of the solid particles. Besides, lower combustion temperature achieved in low engine
5
Fuel xxx (xxxx) xxxx
W. Yu, et al.
Fig.6. Particle size distribution with different engine loads fueled with (a) diesel and (b) Jet A-1.
possible reduction of accumulation mode particles formation [34]. This also can be revealed by the particle number concentrations comparison between Jet A-1 and diesel in Fig. 10, which indicating that particle number concentrations of Jet A-1 is much less than diesel, especially for the accumulation mode particles. It should be noted that, in diesel engine combustion, the accumulation mode particles dominate most of the mass of PM emissions due to their large size compared with nucleation mode particles. Moreover, most operating conditions of diesel engines are under high load. As such, the tremendous reduction in accumulation mode particles for Jet A-1 under high engine load can bring greatly reduction in PM emissions for diesel engine combustion. Although Jet A-1 combustion generate more nucleation mode particles than diesel under low engine load, due to the fact that the nucleation mode particles are mainly composed of unburned HC, so they are easy to remove using a Diesel Oxidation Catalyst (DOC) in an automotive diesel engine [35] or using a Catalytic Stripper (CS) in a marine engine [36]. Therefore, it can be concluded that Jet A-1 has great potential in PM reduction when applied in diesel engines, while the fuel economy is obviously improved without deterioration of NOx emission.
Jet A-1 is at the same level with that of diesel, while the difference of the accumulation mode particle number concentrations between Jet A1 and diesel are much less than that under 70% engine load. Fig. 9 shows particle size distribution under 70% load. When the engine is running under 70% load condition, an intensive diffusive combustion process is achieved as mentioned above. This intensifies the particle formation process and finally results in an obvious increase in the accumulation mode particles. Due to the enhanced surface growth and coagulation processes, as well as more adsorbed nucleation mode particles on the accumulation mode particles, the particle size distribution under 70% load is dominated by accumulation mode while the nucleation mode particles are in turn significantly reduced. The particle number concentrations of accumulation mode particles shown in Fig. 10 (a), (a1), (b) and (b1) can intuitively reflect the fact of this phenomenon: the particle number concentrations of accumulation mode particles are much higher that of nucleation mode particles under 70% engine load. It also can be found out that the accumulation mode particles of Jet A-1 are much less than diesel under 70% engine load, which indicates that Jet A-1 forms much less carbonaceous soot particles. This is probably because, firstly, Jet A-1 has lower aromatic content (18.8%) than diesel (35%) as aromatics are widely held to be immediate soot precursors [6]. Secondly, the Jet A-1 spray undergoes atomization more easily due to its lower viscosity than diesel for better fuel-air mixing, which implies fewer fuel-rich pockets in the combustion chamber and
4. Conclusions In this study, a comprehensive investigation of combustion and emission characteristics of Jet A-1 applied in diesel engine was
Fig. 7. Particle size distribution under 30% load with injection pressure of (a) 600 bar and (b) 800 bar. 6
Fuel xxx (xxxx) xxxx
W. Yu, et al.
Fig. 8. Particle size distribution under 50% load with injection pressure of (a) 600 bar and (b) 800 bar.
combustion duration leading to shorter time for oxidation, HC emission from Jet A-1 is therefore higher than that from diesel. Fuel economy with Jet A-1 is significantly improved compared with diesel, which is because of higher low heating value of Jet A-1 as well as more intensive heat release and higher local combustion temperature. (3) Jet A-1 and diesel show similar trends in the particle size distribution along with the change of engine loads. Under the low engine load, the particle size distribution is dominated by nucleation mode. This is because when the engine is running under low load condition, the less fuel injection leads the local equivalence ratios towards leaner conditions, significantly limiting the formation process of the solid particles. Besides, lower combustion temperature achieved in lower engine load prefers the formation of the nucleation particles. Compared with diesel, higher nucleation particle mode is observed when fueled with Jet A-1 under low engine load. One of the reasons could be related with higher HC emission, while another reason is the lower carbon number in Jet A-1 than that of diesel. (4) As the engine load increases, the equivalence ratio is increased because of more injected fuel mass. In addition, the combustion mode transits from premixed dominated combustion to diffusion combustion with relatively high combustion temperature. Once more nuclei-precursor particles are available, the process of surface growth and coagulation would be therefore enhanced. As such, the
experimentally conducted. Analysis is emphasized on engine performance and soot particle emission both in size and number concentrations when fuelled with Jet A-1, compared with traditional diesel fuel. The potential to improve fuel economy and reduce PM emissions by applying Jet A-1 in the diesel engine was proposed. The results are concluded as follows. (1) As the increase of the injection pressure, the in-cylinder pressure increases and the heat release rate is advanced = for both jet A-1 and diesel fuels. Compared with diesel combustion, the combustion phase is obviously retarded when fueled with Jet A-1, which is mainly related with the lower cetane number of Jet A-1. The proportion of premixed combustion by Jet A-1 is increased along with higher peak of the premixed heat release compared to diesel combustion under different injection pressures and engine loads. This is mainly attributed to more accumulation of fuel in combustion chamber before ignition caused by the increased ignition delays when fueled with Jet A-1. Besides, another reason is that the Jet A-1 which has a lower viscosity than diesel, which undergoes atomization more easily and experiences a shorter penetration with a wider spray angle. (2) NOx emission from Jet A-1 combustion is about 10% higher than that from diesel combustion under 30% engine load, while NOx emissions from both Jet A-1 and diesel combustion are almost the same under 50% and 70% engine loads. Because Jet A-1 has shorter
Fig. 9. Particle size distribution under 70% load with injection pressure of (a) 600 bar and (b) 800 bar. 7
Fuel xxx (xxxx) xxxx
W. Yu, et al.
Fig. 10. Particle number concentrations of different modes with injection pressure of 600 bar and 800 bar (nucleation mode particle number concentration: (a) 600 bar and (a1) 800 bar, accumulation mode particle number concentration: (b) 600 bar and (b1) 800 bar, total particle number concentration: (c) 600 bar and (c1) 800 bar).
8
Fuel xxx (xxxx) xxxx
W. Yu, et al.
accumulation mode particles are increased. Moreover, as the accumulation mode particles increases, the gases that synthesizes nucleation particles are more likely adsorbed on the accumulation particles which results in the reduction of nucleation particles as engine load increases. (5) When the engine is running under high engine load, the particle size distribution is dominated by accumulation mode. The accumulation mode particles of Jet A-1 are much less than diesel under high engine load. It should be noted that, in diesel engine combustion, the accumulation mode particles dominates most of the mass of PM emissions due to the large size of accumulation mode particles. Moreover, most operating conditions of diesel engines are under high load. As such, the tremendous reduction in accumulation mode particles for Jet A-1 under high engine load can bring greatly reduction in PM emissions in diesel engine combustion. (6) Although Jet A-1 combustion generate more nucleation mode particles than diesel under low engine load, they are easy to be removed using exhaust catalytic after treatment. In conclusion, Jet A1 has great potential in PM reduction when applied in diesel engines, while the fuel economy is obviously improved and the NOx emission is not deteriorating.
2014-01-9077. [12] Hui X, Kumar K, Sung C-J, Edwards T, Gardner D. Experimental studies on the combustion characteristics of alternative jet fuels. Fuel 2012;98:176–82. [13] Pickett LM, Hoogterp L. Fundamental spray and combustion measurements of JP-8 at diesel conditions. SAE 2008-01-1083. [14] Park Y, Bae C, Mounaïm-Rousselle C, Foucher F. Application of jet propellant-8 to premixed charge ignition combustion in a single-cylinder diesel engine. Int J Engine Res 2015;16:92–103. [15] Jing W, Roberts WL, Fang T. Spray combustion of Jet-A and diesel fuels in a constant volume combustion chamber. Energy Convers Manage 2015;89:525–40. [16] Kang D, Kalaskar V, Kim D, Martz J, Violi A, Boehman A. Experimental study of autoignition characteristics of Jet-A surrogates and their validation in a motored engine and a constant-volume combustion chamber. Fuel 2016;184:565–80. [17] Song L, Liu T, Fu W, Lin Q. Experimental study on spray characteristics of ethanolaviation kerosene blended fuel with a high-pressure common rail injection system. J Energy Inst 2016. [18] Yu W, Yang W, Mohan B, Tay K, Zhao F, Zhang Y, et al. Numerical and Experimental Study on Internal Nozzle Flow and Macroscopic Spray Characteristics of a Kind of Wide Distillation Fuel (WDF)-Kerosene. SAE 2016-01-0839. [19] Yu W, Yang W, Zhao F. Investigation of internal nozzle flow, spray and combustion characteristics fueled with diesel, gasoline and wide distillation fuel (WDF) based on a piezoelectric injector and a direct injection compression ignition engine. Appl Therm Eng 2017;114:905–20. [20] Lee J, Lee J, Chu S, Choi H, Min K. Emission reduction potential in a light-duty diesel engine fueled by JP-8. Energy 2015;89:92–9. [21] https://www.cambustion.com/. [22] Sinharay R, Gong J, Barratt B, Ohman-Strickland P, Ernst S, Kelly F, et al. Respiratory and cardiovascular re-sponses to walking down a traffic-polluted road compared with walking in atraffic-free area in participants aged 60 years and older with chronic lung orheart disease and age-matched healthy controls: a randomised, crossoverstudy. Lancet 2017;6736:1–11. [23] Brown JS, Gordon T, Price O, Asgharian B. Thoracic and respirable particledefinitions for human health risk assessment. Part Fibre Toxicol 2013;10:12. [24] Nargunde Jagdish, Chandrasekharan Jayakumar, Anubhav Sinha, Kaushik Acharya, Walter Bryzik, Naeim Henein. Comparison between combustion, performance and emission characteristics of JP-8 and ultra low sulfur diesel fuel in a single cylinder diesel engine. SAE 2010-01-1123. [25] Boichenko SV, Leida K, Yakovleva AV, Vovk OA, Kuzhevskii K. Influence of rapeseed oil ester additives on fuel quality index for air jet engines. Chem Technol Fuels Oils 2017;53(3):308–17. [26] Yu W, Yang W, Tay K, Mohan B, Zhao F, Zhang Y. Macroscopic spray characteristics of kerosene and diesel based on two different piezoelectric and solenoid injectors. Exp Therm Fluid Sci 2016;76:12–23. [27] Chen K, Liu H, Xia, Z. The Impacts of Aromatic Contents in Aviation Jet Fuel on the Volume Swell of the Aircraft Fuel Tank Sealants. SAE 2013-01-9001. [28] Yu W, Yang W, Mohan B, Tay KL, Zhao F. Macroscopic spray characteristics of wide distillation fuel (WDF). Appl Energy 2017;185:1372–82. [29] Lin Tay K, Yu W, Zhao F, Yang W. From fundamental study to practical application of kerosene in compression ignition engines: an experimental and modeling review. Proc Inst Mech Eng, Part D: J Automobile Eng 2019. 0954407019841218. [30] Saxena MR, Maurya RK. Effect of premixing ratio, injection timing and compression ratio on nano particle emissions from dual fuel non-road compression ignition engine fueled with gasoline/methanol (port injection) and diesel (direct injection). Fuel 2017;203:894–914. [31] Schonbom A, Ladommatos N, Allan R, Williams J, Rogerson J. Effect of the molecular structure of individual fatty acid alcohol esters (biodiesel) on the formation of NOx and particulate matter in the diesel combustion process. SAE Int J Fuels Lubr 2009;1:849–72. [32] Murat HT, Jun W, Yiannis AL, Joel BC, Joseph J. PAH and other emissions from burning of JP-8 and diesel fuels in diffusion flames. Fuel 2004;83:2537–68. [33] Reijnders J, Boot M, de Goey P. Particle nucleation-accumulation mode trade-off: A second diesel dilemma? J Aerosol Sci 2018;124:95–111. [34] Fernandes G, Fuschetto J, Filipi Z, Assanis D, McKee H. Impact of military JP-8 fuel on heavy-duty diesel engine performance and emissions. Proc Inst Mech Eng, Part D: J Automobile Eng. 2007;221(8):957–70. [35] Yusop AF, Mamat R, Mat Yasin MH, Ali OM. Effects of particulate matter emissions of diesel engine using diesel–methanol blends. J Mech Eng Sci 2014;6:959–67. [36] Johnson K, Miller W, Durbin T, Jiang Y, Yang J, Karavalakis G, et al. Black carbon measurement methods and emission factors from ships. Riverside: University of California; 2016.
Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements Support from the National Research Foundation (NRF) of Singapore under research grant WBS R-265-000-611-281 is gratefully acknowledged. References [1] Xing F, Kumar A, Huang Y, Chan S, Ruan C, Gu S, et al. Flameless combustion with liquid fuel: a review focusing on fundamentals and gas turbine application. Appl Energy 2017;193:28–51. [2] Li S, Ge Y, Wei X, Li T. Mixing and combustion modeling of hydrogen peroxide/ kerosene shear-coaxial jet flame in lab-scale rocket engine. Aerosp Sci Technol 2016;56:148–54. [3] Lee J, Bae C. Application of JP-8 in a heavy duty diesel engine. Fuel 2011;90:1762–70. [4] Bowden J, Westbrook S, LePera M. Jet kerosene fuels for military diesel application. SAE 892070. [5] Administration USEI. Petroleum & other liquids. 2019. [6] Heywood JB. Internal combustion engine fundamentals. New York: Mcgraw-hill; 1988. [7] Crippa M, Janssens-Maenhout G, Guizzardi D, Galmarini S. EU effect: Exporting emission standards for vehicles through the global market economy. J Environ Manage 2016;183:959–71. [8] Zhang C, Li B, Rao F, Li P, Li X. A shock tube study of the autoignition characteristics of RP-3 jet fuel. Proc Combust Inst 2015;35:3151–8. [9] Zhu Y, Li S, Davidson DF, Hanson RK. Ignition delay times of conventional and alternative fuels behind reflected shock waves. Proc Combust Inst 2015;35:241–8. [10] Wang H, Oehlschlaeger MA. Autoignition studies of conventional and FischerTropsch jet fuels. Fuel 2012;98:249–58. [11] Shrestha A, Zheng Z, Badawy T, Henein N, Schihl P. Development of JP-8 surrogates and their validation using ignition quality tester. SAE Int J Fuels Lubricants: SAE
9
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Full Length Article
Experimental study on engine combustion and particle size distributions fueled with Jet A-1 ⁎
⁎
Wenbin Yua, Yichen Zonga, Qinjie Lina, Kunlin Taya, Feiyang Zhaoa, , Wenming Yanga, , Markus Kraftb,c a
Department of Mechanical Engineering, National University of Singapore, Singapore School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore c Department of Chemical Engineering and Biotechnology, University of Cambridge, United Kingdom b
A R T I C LE I N FO
A B S T R A C T
Keywords: Jet A-1 Particle mode Particle size distribution Particle number concentration Particulate matter
In this study, a comprehensive investigation of combustion and emission characteristics of Jet A-1 applied in diesel engine was experimentally conducted. Analysis is emphasized on engine performance and soot particle emission both in size and number concentrations when fueled with Jet A-1, compared with traditional diesel fuel. It is concluded that compared with diesel combustion, the combustion phase is obviously retarded when fueled with Jet A-1. The premixed combustion fraction with Jet A-1 is increased and the peak of premixed heat release of Jet A-1 is higher compared with diesel combustion under different injection pressures and different engine loads. Fuel economy with Jet A-1 is significantly improved compared with diesel, which is because of higher low heating value of Jet A-1 as well as more intensive heat release near top dead center (TDC). Jet A-1 and diesel show similar trends in particle size distribution along with the changes of engine loads. Under the low engine load, the particle size distribution is basically dominated by nucleation mode, meanwhile higher concentration of nucleation particles is observed when fueled with Jet A-1 compared to diesel. As the engine load increases, the accumulation particles are increased while the nucleation particles are in turn decreased. When the engine is running under high engine load, the particle size distribution is dominated by accumulation mode. Based on these findings, the potential to improve fuel economy and reduce particulate matter (PM) emissions by using Jet A-1 in a diesel engine was therefore proposed.
1. Introduction Jet fuel is becoming more and more important in industrial and military applications. It is used not only for the rocket engines [1] and gas turbine engines [2] but also for diesel engines [3]. One of the reasons of the usage of jet fuel in diesel engines is the Single Fuel Concept (SFC) introduced by the United Sates army military, which could help to improve and simplify the fuel supply chain during both wartime and peacetime [4]. The other reason is that the aviation jet fuel is cheaper than diesel. As reported in 2017, the price of aviation jet fuel is US$1.558/gallon while the ultra-low-sulphur diesel is US$1.620/ gallon [5]. Diesel engines are widely used for both civilian and military applications due to the high thermal efficiency as well as the high torque relative to the gasoline engine [6]. However, compared with gasoline engine, the shortcoming of the diesel engine is also more obvious in the aspects of exhaust emissions, especially the PM emissions [6]. Over
⁎
decades, strict emissions standards [7] were implemented to regulate diesel engine emissions. The traditional diesel engines are developed specifically for diesel fuel, as such, the usage of other alternative fuels in diesel engines with different fuel properties such as jet fuel must be deeply investigated in case of adverse effects on engine emissions. A deep understanding of the jet fuel autoignition characteristics, jet fuel spray and spray-guided combustion are important for its successful usage in diesel engines. In the past years, lots of researchers investigated the autoignition characteristics using different equipment including shock tube, rapid compression machine (RCM), fuel ignition tester (FIT), ignition quality tester (IQT), constant volume combustion chamber (CVCC) and engines [8–13]. Various researchers had contributed significant studies on the constant volume spray and combustion of jet fuel, such as Pickett and Hoogterp [13], Lee and Bae [3], Park et al. [14], Jing et al. [15], Kang et al. [16], Song et al. [17] and the authors’ research group [18,19]. In recent years, lots of investigations on engine combustion and emissions fueled with jet fuel have been
Corresponding authors. E-mail addresses: [email protected] (F. Zhao), [email protected] (W. Yang).
https://doi.org/10.1016/j.fuel.2019.116747 Received 11 July 2019; Received in revised form 30 October 2019; Accepted 24 November 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Wenbin Yu, et al., Fuel, https://doi.org/10.1016/j.fuel.2019.116747
Fuel xxx (xxxx) xxxx
W. Yu, et al.
carried out. Lee et al. [3] reported that jet fuel combustion in a diesel engine had a longer ignition delay than diesel, which is primarily due to its lower CN. By using EGR along with optimized injection strategies, further optimization for both NOx and soot emissions from jet fuel combustion was proven to be possible without loss of efficiency [20]. The three most common used conventional jet fuels are Jet-A, Jet A1 and JP-8. Jet A is used only in the United State while Jet A-1 is used throughout the rest of the world [4]. The freezing point of Jet A is at −40 °C while that of Jet A-1 is at −47 °C [4]. Currently, although some engine experimental works fueled with jet fuel such as JP8 had been done, however, there are no researchers to do comprehensive and indepth investigations on PM emissions including particle size distribution and number concentration when fueled with Jet A-1 in diesel engines. In order to bridge this research gap, in this study, an engine experimental study fueled with Jet A-1 and diesel was conducted. A comprehensive investigation regarding the effect of engine parameters and fuel properties on engine performance, combustion process, particle size distribution and particle number concentration was done. Hence, the key factors that influence the particle emissions when fueled with Jet A-1 could be consequently figured out.
Table 1 Engine specifications. Brand
Yanmar
Bore × Stroke Displacement Compression Ratio Injection system Injection Pressure Rated output power
92 × 96 mm 0.638 L 17.7 Common rail 200 MPa Max. 7.8/2400 kW/rpm
current can be calibrated to adapt varied brands injectors from open market. It can also control common rail pressure, throttle valve, exhaust gas recirculation (EGR) valve, variable-geometry turbocharger (VGT), et al. Besides, the control system can be used to simulate a virtual engine to validate control strategies. A real-time combustion analysis, data acquisition and diagnosis system, which was embedded in the next-cycle control system, was used for the diagnosis of engines and engine relevant components such as all kinds of sensors and electronic control actuators. Same with the work done by Nargunde Jagdish et al. in 2010 [24], in this study, apparent heat release rate (AHRR) is calculated from incylinder pressure curve during the firing of the engine after subtracting the heat release rate during motoring under same cylinder wall temperature conditions. The motoring heat release rate trace was recorded by interrupting the fuel supply for a few numbers of cycles momentarily during the steady state condition. This was done in an effort to maintain the same cylinder wall temperature for both firing and motoring. The data acquisition software uses following formula to calculate the AHRR at any given crank angle degree [6].
2. Experimental procedures 2.1. Experimental setup The experimental study was conducted on a single-cylinder diesel engine and the schematic of experimental setup can be shown in Fig. 1. The single-cylinder research engine was provided by Yanmar Co., Ltd. while a common rail high pressure fuel injection system from Denso was equipped. Table 1 shows the specifications of the test engine. A next-cycle control system based on combustion analysis was developed in-house for engine control, which can also be seen in Fig. 1. Next-cycle control is the process of rapidly collecting cylinder pressure data and doing the post process for use in a control loop with enough time to adjust engine control parameters and command actuators for the next combustion cycle. With next-cycle control, certain combustion conditions such as crank angle for 50% heat release (CA50) can be targeted and accurately controlled between every cycle of the engine. Field-programmable gate array (FPGA) with the real-time computing hardware are used. This control system is flexible and extendable which can control both piezo and solenoid injectors. It can control injection timing, injection duration and multiple injections, while the injector
γ dp dQn dV 1 = p + V dt γ − 1 dt γ − 1 dt
(1)
Here ‘p’ is cylinder pressure; ‘V’ is swept volume, ‘γ’ is the ratio of specific heats and is assumed as a constant number of 1.4. The concentrations of CO2, CO, O2, NOx and HC in the exhaust gas were measured using a gas analyzer from AVL. The exhaust particle size distribution and number concentration were measured with a Differential Mobility Spectrometer 500 (DMS500) provided by Cambustion Ltd. As stated by Cambustion Ltd [21], the DMS500 uses a high voltage discharge to charge each particle proportional to its surface area. Charged particles are introduced into a classification section with a strong radial electrical field. This field causes particles to drift
Fig.1. Schematic diagrams of experimental setup. 2
Fuel xxx (xxxx) xxxx
W. Yu, et al.
through a sheath flow toward the electrometer detectors. Particles are detected at different distances down the column, depending upon their aerodynamic drag/charge ratio. Outputs from the 22 electrometers are processed in real-time at 10 Hz to provide a number/size spectrum for particles between 5 and 1000 nm.
Table 3 Fuel properties. Properties 3
Density at 15 °C (kg/m ) Viscosity at 40 °C (mm2/s) Cetane number Aromatics (vol%) Low Calorific value (MJ/Kg) Flash point (°C)
2.2. Particle size analysis Air pollution now is presenting a big challenge for the sustainable development of the entire world. It has been pointed out that long term exposure to ambient fine particulates (< 1000 nm) is associated with increased mortality and morbidity from diseases of pulmonary and cardiovascular [22]. Epidemiological investigations also revealed that ultrafine particles (< 100 nm) from soot emissions may have sever adverse health effects, considering their larger likelihood of penetration and higher surface area per unit volume to adsorb organic compounds [23]. In our present work, in order to do detailed analysis, the particle size distribution is separated into two regions including nucleation mode (2–50 nm) and accumulation mode (50–300 nm), which is the same with the previous investigation done in 2010 [24]. Such classification is useful for a deeper understanding of the effect of various engine parameters on PM emissions.
Diesel
804 1.13 [25] 42 18.8% [27] 43.2 38
831 3 [26] 52 35% [24] 42.7 55
the two injection pressures and test engine loads. This can also be revealed intuitively by the CA50 in comparison between Jet A-1 and diesel in Fig. 3. This phenomenon is mainly related with the lower cetane number of Jet A-1 (Jet A-1:42, diesel: 52) [20]. The AHRR curves also indicate that the fraction of premixed combustion by Jet A-1 is increased with higher peak compared to diesel combustion under test injection pressures and engine loads. This is mainly attributed to more accumulation of fuel in combustion chamber before ignition caused by the increased ignition delay when fueled with Jet A-1. Besides, another reason is that the Jet A-1 which has a lower viscosity than diesel (shown in Table 3) undergoes atomization more easily and therefore experiences a shorter penetration with a wider spray angle, which can be deduced from the authors’ previous spray study of Jet fuel [26,28,29]. As shown in Fig. 4, under low (30%) engine load, NOx emission from Jet A-1 combustion is about 10% higher than that from diesel combustion due to higher premixed combustion fraction of Jet A-1. However, based on the heat release traces comparison in Fig. 2 it can be seen that, both Jet A-1 and diesel combustion at middle (50%) and high (70%) engine loads are typically dominated by diffusion combustion, which present lower premixed combustion fraction than the low (30%) engine load. As such, NOx emission from Jet A-1 combustion is almost the same with that from diesel combustion at middle (50%) and high (70%) engine loads because the NOx emission here is mainly from diffusion combustion. Fig. 5 shows the HC emission comparison between Jet A-1 and diesel under different engine loads, injection timings and injection pressures. It should be noted that the final HC emissions are the result of the combined influence of many factors such as the spray, atomization, fuel properties, combustion temperature and fuelair equivalence ratio. In this study, the HC emission from Jet A-1 combustion is higher than diesel, as shown in Fig. 5. Firstly, the main reason is that a locally fuel-lean mixture with Jet A-1 was formed mainly due to the longer ignition and higher volatility [14]. In terms of the combustion regime, higher HC emission was obtained with premixed dominated combustion from the over-lean mixture by the longer mixing time. Similar result and explanation were also concluded by Park Y et al. [14]. Secondly, it also can be seen in Fig. 2 that in all cases the onset of heat release profile of Jet A-1 is retarded, but combustion ends at the same time. This indicates that Jet A-1 has shorter combustion duration leading to shorter time for fuel oxidation, which can also explain the phenomenon that the HC emission from Jet A-1 is higher than diesel. Table 4 shows that the indicated specific fuel consumption (ISFC) with different engine loads, injection timings and injection pressures. It can be seen that the fuel consumption is generally improved when fueled with Jet A-1. The largest improvement is 2.71% which is under 70% engine load, while the average improvement for all cases shown in Table 4 is around 1.84%. Firstly, the higher low heating value of Jet A-1 compared to diesel is one of the contributions to the better fuel economy. Secondly, the peak of the premixed heat release of Jet A-1 is higher and the premixed combustion fraction with Jet A-1 is increased compared with diesel combustion, leading to more concentrated heat release and higher local combustion temperature, which may help to improve the indicated thermal efficiency of the diesel engine combustion.
2.3. Experimental conditions In this study, the engine speed is fixed at 1400 rpm and three different engine loads of 30%, 50% and 70% were selected to represent low, middle and high engine loads to investigate the engine combustion process, exhaust gas and PM emissions characteristics of Jet A-1, comparing to traditional diesel fuel. The maximum output torque for this single-cylinder diesel engine at 1400 rpm is 40 Nm, so the absolute engine torque is 12, 20 and 28 Nm under three engine loads respectively. In the study, the experiment is conducted based on the torque which can be read by the dynamometer, this means, for a constant engine load, the injection amount may be different because of the application of different fuels and different injection pressures. In the experiment, the cycle change of the engine load varies within 5%. Besides, two injection pressures of 600, 800 bar and three start of injection timings (SOI) of −5, 0, 5 deg.ATDC were selected in the engine experiment. The experimental conditions and fuel properties can be seen in Tables 2 and 3 respectively. 3. Results and discussion 3.1. Combustion and gas emissions characteristics of Jet A-1 Fig. 2 indicates the in-cylinder pressure and AHRR for Jet A-1 and diesel under two injection pressures (600, 800 bar) and three engine loads (30%, 50%, 70%). The start of injection timing is fixed at 0 deg.ATDC. It is evident that the in-cylinder pressure increases and the heat release rate is becoming advanced with the increase of the injection pressure for both jet A-1 and diesel. This is because faster fuel spray, smaller droplet atomization and better fuel-air mixing can enhance the fuel premixed combustion under higher injection pressures. It can be seen in Fig. 2 that, compared with diesel combustion, the combustion phase is obviously retarded when fueled with Jet A-1 under Table 2 Experimental conditions. Speed Load Intake pressure Injection pressure Injection strategy Start of injection timing (SOI) Test fuels
Jet A-1
1400 rpm 30%, 50%, 70% Ambient pressure 600, 800 bar Single injection −5, 0, 5 deg.ATDC Jet A-1, diesel
3
Fuel xxx (xxxx) xxxx
W. Yu, et al.
Fig. 2. In-cylinder pressure and AHRR traces with different injection pressures under engine loads of (a) 30%, (b) 50% and (c) 70% (SOI: 0 deg.ATDC).
Fig. 3. CA50 with different engine loads and injection timings under injection pressures of (a) 600 bar and (b) 800 bar.
Fig. 4. NOx emissions with different engine loads and injection timings under injection pressures of (a) 600 bar and (b) 800 bar. 4
Fuel xxx (xxxx) xxxx
W. Yu, et al.
Fig. 5. HC emissions with different engine loads and injection timings under injection pressures of (a) 600 bar and (b) 800 bar.
load, which can be deduced from the lower in-cylinder pressures compared to higher engine loads as seen in Fig. 2, prefers the formation of the nucleation particles [30]. It should be noted that, compared with diesel, more nucleation mode particles can be observed when fueled with Jet A-1 under 30% load without significant variations for the different injection timings and injection pressures, as seen in Fig. 7. One of the reasons could be related with higher HC emission of Jet A-1 caused by more intensive premixed combustion [13,31]. In addition, due to lower carbon number of Jet A-1 than that of diesel, the Jet A-1 combustion more favours nucleation mode particles under the conditions of leaner combustion or lower temperature combustion [32]. Moreover, higher concentrations of nucleation mode particles from Jet A-1 combustion can also reflect the fact that the HC emission from Jet A-1 is higher than diesel under some certain conditions. Fig. 10 shows the particle number concentrations of different modes under different engine loads and injection pressures. It can be seen in Fig. 10(a), (a1), (b) and (b1) intuitively that under 30% engine load condition the particle number concentration of nucleation mode particles is much more than that of accumulation mode particles, which reveals that the particles under 30% engine load are dominated by nucleation mode without significant variations for different injection timings and injection pressures. When the engine is running under 50% load conditions, more injected fuel leads to an increase of local equivalence ratios. Besides, the combustion mode obviously transits from premixed dominated combustion to diffusion combustion along with higher combustion temperature, which promotes the nuclei-precursor particles formation process. Once more nuclei particles are available, the subsequent surface growth and coagulation processes are therefore enhanced [33]. The depiction here can help to explain that under 50% load condition, the nucleation mode particles are decreased compared with 30% engine load, while the accumulation mode particles are increased to some extent, as seen in Fig. 6. Accumulation mode particles in combustion are known to act as adsorption site for the gases responsible for the formation of the nucleation mode particles, which means as the accumulation mode particles increase, the gases that synthesizes nucleation mode particles are more likely to be adsorbed on the accumulation particles. This is also another reason for the reduction of the nucleation particles. Finally, it can be seen in Fig. 8 that in all cases the nucleation mode particles of Jet A-1 and diesel are at almost the same level as well as the accumulation mode particles. This can also be intuitively shown in Fig. 10 by the statistics of particle number concentrations of different particle modes: the nucleation mode particle number concentration of
Table 4 ISFC with different engine loads, injection timings and injection pressures. Engine load (%)
Injection pressure (bar)
SOI (deg.ATDC)
ISFCd (g/kWh)
ISFCJ (g/kWh)
(ISFCJ – ISFCd)/ ISFCd *100% (%)
30%
600
−5 0 5 −5 0 5 −5 0 5 −5 0 5 −5 0 5 −5 0 5
226.51 218.50 218.03 233.08 217.39 207.37 201.58 200.16 198.83 205.30 199.78 199.89 196.46 199.25 202.85 197.46 194.79 197.84
220.52 214.65 216.23 228.82 213.98 203.62 197.67 195.06 195.33 201.93 194.53 198.66 194.19 195.96 200.15 192.77 190.20 192.48
−2.64 −1.76 −0.83 −1.83 −1.57 −1.81 −1.94 −2.55 −1.76 −1.64 −2.63 −0.62 −1.16 −1.65 −1.33 −2.37 −2.36 −2.71
800
50%
600
800
70%
600
800
ISFCd and ISFCJ stand for ISFC of diesel and Jet A-1 respectively.
3.2. Particulate matter emission characteristics of Jet A-1 Fig. 6 shows the particle size distribution with different engine loads, indicating that Jet A-1 and diesel present similar trends in the particle size distribution along with the changes of engine loads: (1) Under the low engine load (30% load), the particle size distribution is mainly dominated by nucleation mode. (2) Under the middle engine load (50% load), the proportion of nucleation mode particles are decreased compared with 30% engine load. The nucleation mode and accumulation mode are almost at the same level. (3) Under the high engine load (70% load), the particle size distribution is typically dominated by accumulation mode. When the engine is running under 30% engine load condition, the less fuel injection leads the local equivalence ratios towards lean-conditions, significantly limiting the formation process of the solid particles. Besides, lower combustion temperature achieved in low engine
5
Fuel xxx (xxxx) xxxx
W. Yu, et al.
Fig.6. Particle size distribution with different engine loads fueled with (a) diesel and (b) Jet A-1.
possible reduction of accumulation mode particles formation [34]. This also can be revealed by the particle number concentrations comparison between Jet A-1 and diesel in Fig. 10, which indicating that particle number concentrations of Jet A-1 is much less than diesel, especially for the accumulation mode particles. It should be noted that, in diesel engine combustion, the accumulation mode particles dominate most of the mass of PM emissions due to their large size compared with nucleation mode particles. Moreover, most operating conditions of diesel engines are under high load. As such, the tremendous reduction in accumulation mode particles for Jet A-1 under high engine load can bring greatly reduction in PM emissions for diesel engine combustion. Although Jet A-1 combustion generate more nucleation mode particles than diesel under low engine load, due to the fact that the nucleation mode particles are mainly composed of unburned HC, so they are easy to remove using a Diesel Oxidation Catalyst (DOC) in an automotive diesel engine [35] or using a Catalytic Stripper (CS) in a marine engine [36]. Therefore, it can be concluded that Jet A-1 has great potential in PM reduction when applied in diesel engines, while the fuel economy is obviously improved without deterioration of NOx emission.
Jet A-1 is at the same level with that of diesel, while the difference of the accumulation mode particle number concentrations between Jet A1 and diesel are much less than that under 70% engine load. Fig. 9 shows particle size distribution under 70% load. When the engine is running under 70% load condition, an intensive diffusive combustion process is achieved as mentioned above. This intensifies the particle formation process and finally results in an obvious increase in the accumulation mode particles. Due to the enhanced surface growth and coagulation processes, as well as more adsorbed nucleation mode particles on the accumulation mode particles, the particle size distribution under 70% load is dominated by accumulation mode while the nucleation mode particles are in turn significantly reduced. The particle number concentrations of accumulation mode particles shown in Fig. 10 (a), (a1), (b) and (b1) can intuitively reflect the fact of this phenomenon: the particle number concentrations of accumulation mode particles are much higher that of nucleation mode particles under 70% engine load. It also can be found out that the accumulation mode particles of Jet A-1 are much less than diesel under 70% engine load, which indicates that Jet A-1 forms much less carbonaceous soot particles. This is probably because, firstly, Jet A-1 has lower aromatic content (18.8%) than diesel (35%) as aromatics are widely held to be immediate soot precursors [6]. Secondly, the Jet A-1 spray undergoes atomization more easily due to its lower viscosity than diesel for better fuel-air mixing, which implies fewer fuel-rich pockets in the combustion chamber and
4. Conclusions In this study, a comprehensive investigation of combustion and emission characteristics of Jet A-1 applied in diesel engine was
Fig. 7. Particle size distribution under 30% load with injection pressure of (a) 600 bar and (b) 800 bar. 6
Fuel xxx (xxxx) xxxx
W. Yu, et al.
Fig. 8. Particle size distribution under 50% load with injection pressure of (a) 600 bar and (b) 800 bar.
combustion duration leading to shorter time for oxidation, HC emission from Jet A-1 is therefore higher than that from diesel. Fuel economy with Jet A-1 is significantly improved compared with diesel, which is because of higher low heating value of Jet A-1 as well as more intensive heat release and higher local combustion temperature. (3) Jet A-1 and diesel show similar trends in the particle size distribution along with the change of engine loads. Under the low engine load, the particle size distribution is dominated by nucleation mode. This is because when the engine is running under low load condition, the less fuel injection leads the local equivalence ratios towards leaner conditions, significantly limiting the formation process of the solid particles. Besides, lower combustion temperature achieved in lower engine load prefers the formation of the nucleation particles. Compared with diesel, higher nucleation particle mode is observed when fueled with Jet A-1 under low engine load. One of the reasons could be related with higher HC emission, while another reason is the lower carbon number in Jet A-1 than that of diesel. (4) As the engine load increases, the equivalence ratio is increased because of more injected fuel mass. In addition, the combustion mode transits from premixed dominated combustion to diffusion combustion with relatively high combustion temperature. Once more nuclei-precursor particles are available, the process of surface growth and coagulation would be therefore enhanced. As such, the
experimentally conducted. Analysis is emphasized on engine performance and soot particle emission both in size and number concentrations when fuelled with Jet A-1, compared with traditional diesel fuel. The potential to improve fuel economy and reduce PM emissions by applying Jet A-1 in the diesel engine was proposed. The results are concluded as follows. (1) As the increase of the injection pressure, the in-cylinder pressure increases and the heat release rate is advanced = for both jet A-1 and diesel fuels. Compared with diesel combustion, the combustion phase is obviously retarded when fueled with Jet A-1, which is mainly related with the lower cetane number of Jet A-1. The proportion of premixed combustion by Jet A-1 is increased along with higher peak of the premixed heat release compared to diesel combustion under different injection pressures and engine loads. This is mainly attributed to more accumulation of fuel in combustion chamber before ignition caused by the increased ignition delays when fueled with Jet A-1. Besides, another reason is that the Jet A-1 which has a lower viscosity than diesel, which undergoes atomization more easily and experiences a shorter penetration with a wider spray angle. (2) NOx emission from Jet A-1 combustion is about 10% higher than that from diesel combustion under 30% engine load, while NOx emissions from both Jet A-1 and diesel combustion are almost the same under 50% and 70% engine loads. Because Jet A-1 has shorter
Fig. 9. Particle size distribution under 70% load with injection pressure of (a) 600 bar and (b) 800 bar. 7
Fuel xxx (xxxx) xxxx
W. Yu, et al.
Fig. 10. Particle number concentrations of different modes with injection pressure of 600 bar and 800 bar (nucleation mode particle number concentration: (a) 600 bar and (a1) 800 bar, accumulation mode particle number concentration: (b) 600 bar and (b1) 800 bar, total particle number concentration: (c) 600 bar and (c1) 800 bar).
8
Fuel xxx (xxxx) xxxx
W. Yu, et al.
accumulation mode particles are increased. Moreover, as the accumulation mode particles increases, the gases that synthesizes nucleation particles are more likely adsorbed on the accumulation particles which results in the reduction of nucleation particles as engine load increases. (5) When the engine is running under high engine load, the particle size distribution is dominated by accumulation mode. The accumulation mode particles of Jet A-1 are much less than diesel under high engine load. It should be noted that, in diesel engine combustion, the accumulation mode particles dominates most of the mass of PM emissions due to the large size of accumulation mode particles. Moreover, most operating conditions of diesel engines are under high load. As such, the tremendous reduction in accumulation mode particles for Jet A-1 under high engine load can bring greatly reduction in PM emissions in diesel engine combustion. (6) Although Jet A-1 combustion generate more nucleation mode particles than diesel under low engine load, they are easy to be removed using exhaust catalytic after treatment. In conclusion, Jet A1 has great potential in PM reduction when applied in diesel engines, while the fuel economy is obviously improved and the NOx emission is not deteriorating.
2014-01-9077. [12] Hui X, Kumar K, Sung C-J, Edwards T, Gardner D. Experimental studies on the combustion characteristics of alternative jet fuels. Fuel 2012;98:176–82. [13] Pickett LM, Hoogterp L. Fundamental spray and combustion measurements of JP-8 at diesel conditions. SAE 2008-01-1083. [14] Park Y, Bae C, Mounaïm-Rousselle C, Foucher F. Application of jet propellant-8 to premixed charge ignition combustion in a single-cylinder diesel engine. Int J Engine Res 2015;16:92–103. [15] Jing W, Roberts WL, Fang T. Spray combustion of Jet-A and diesel fuels in a constant volume combustion chamber. Energy Convers Manage 2015;89:525–40. [16] Kang D, Kalaskar V, Kim D, Martz J, Violi A, Boehman A. Experimental study of autoignition characteristics of Jet-A surrogates and their validation in a motored engine and a constant-volume combustion chamber. Fuel 2016;184:565–80. [17] Song L, Liu T, Fu W, Lin Q. Experimental study on spray characteristics of ethanolaviation kerosene blended fuel with a high-pressure common rail injection system. J Energy Inst 2016. [18] Yu W, Yang W, Mohan B, Tay K, Zhao F, Zhang Y, et al. Numerical and Experimental Study on Internal Nozzle Flow and Macroscopic Spray Characteristics of a Kind of Wide Distillation Fuel (WDF)-Kerosene. SAE 2016-01-0839. [19] Yu W, Yang W, Zhao F. Investigation of internal nozzle flow, spray and combustion characteristics fueled with diesel, gasoline and wide distillation fuel (WDF) based on a piezoelectric injector and a direct injection compression ignition engine. Appl Therm Eng 2017;114:905–20. [20] Lee J, Lee J, Chu S, Choi H, Min K. Emission reduction potential in a light-duty diesel engine fueled by JP-8. Energy 2015;89:92–9. [21] https://www.cambustion.com/. [22] Sinharay R, Gong J, Barratt B, Ohman-Strickland P, Ernst S, Kelly F, et al. Respiratory and cardiovascular re-sponses to walking down a traffic-polluted road compared with walking in atraffic-free area in participants aged 60 years and older with chronic lung orheart disease and age-matched healthy controls: a randomised, crossoverstudy. Lancet 2017;6736:1–11. [23] Brown JS, Gordon T, Price O, Asgharian B. Thoracic and respirable particledefinitions for human health risk assessment. Part Fibre Toxicol 2013;10:12. [24] Nargunde Jagdish, Chandrasekharan Jayakumar, Anubhav Sinha, Kaushik Acharya, Walter Bryzik, Naeim Henein. Comparison between combustion, performance and emission characteristics of JP-8 and ultra low sulfur diesel fuel in a single cylinder diesel engine. SAE 2010-01-1123. [25] Boichenko SV, Leida K, Yakovleva AV, Vovk OA, Kuzhevskii K. Influence of rapeseed oil ester additives on fuel quality index for air jet engines. Chem Technol Fuels Oils 2017;53(3):308–17. [26] Yu W, Yang W, Tay K, Mohan B, Zhao F, Zhang Y. Macroscopic spray characteristics of kerosene and diesel based on two different piezoelectric and solenoid injectors. Exp Therm Fluid Sci 2016;76:12–23. [27] Chen K, Liu H, Xia, Z. The Impacts of Aromatic Contents in Aviation Jet Fuel on the Volume Swell of the Aircraft Fuel Tank Sealants. SAE 2013-01-9001. [28] Yu W, Yang W, Mohan B, Tay KL, Zhao F. Macroscopic spray characteristics of wide distillation fuel (WDF). Appl Energy 2017;185:1372–82. [29] Lin Tay K, Yu W, Zhao F, Yang W. From fundamental study to practical application of kerosene in compression ignition engines: an experimental and modeling review. Proc Inst Mech Eng, Part D: J Automobile Eng 2019. 0954407019841218. [30] Saxena MR, Maurya RK. Effect of premixing ratio, injection timing and compression ratio on nano particle emissions from dual fuel non-road compression ignition engine fueled with gasoline/methanol (port injection) and diesel (direct injection). Fuel 2017;203:894–914. [31] Schonbom A, Ladommatos N, Allan R, Williams J, Rogerson J. Effect of the molecular structure of individual fatty acid alcohol esters (biodiesel) on the formation of NOx and particulate matter in the diesel combustion process. SAE Int J Fuels Lubr 2009;1:849–72. [32] Murat HT, Jun W, Yiannis AL, Joel BC, Joseph J. PAH and other emissions from burning of JP-8 and diesel fuels in diffusion flames. Fuel 2004;83:2537–68. [33] Reijnders J, Boot M, de Goey P. Particle nucleation-accumulation mode trade-off: A second diesel dilemma? J Aerosol Sci 2018;124:95–111. [34] Fernandes G, Fuschetto J, Filipi Z, Assanis D, McKee H. Impact of military JP-8 fuel on heavy-duty diesel engine performance and emissions. Proc Inst Mech Eng, Part D: J Automobile Eng. 2007;221(8):957–70. [35] Yusop AF, Mamat R, Mat Yasin MH, Ali OM. Effects of particulate matter emissions of diesel engine using diesel–methanol blends. J Mech Eng Sci 2014;6:959–67. [36] Johnson K, Miller W, Durbin T, Jiang Y, Yang J, Karavalakis G, et al. Black carbon measurement methods and emission factors from ships. Riverside: University of California; 2016.
Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements Support from the National Research Foundation (NRF) of Singapore under research grant WBS R-265-000-611-281 is gratefully acknowledged. References [1] Xing F, Kumar A, Huang Y, Chan S, Ruan C, Gu S, et al. Flameless combustion with liquid fuel: a review focusing on fundamentals and gas turbine application. Appl Energy 2017;193:28–51. [2] Li S, Ge Y, Wei X, Li T. Mixing and combustion modeling of hydrogen peroxide/ kerosene shear-coaxial jet flame in lab-scale rocket engine. Aerosp Sci Technol 2016;56:148–54. [3] Lee J, Bae C. Application of JP-8 in a heavy duty diesel engine. Fuel 2011;90:1762–70. [4] Bowden J, Westbrook S, LePera M. Jet kerosene fuels for military diesel application. SAE 892070. [5] Administration USEI. Petroleum & other liquids. 2019. [6] Heywood JB. Internal combustion engine fundamentals. New York: Mcgraw-hill; 1988. [7] Crippa M, Janssens-Maenhout G, Guizzardi D, Galmarini S. EU effect: Exporting emission standards for vehicles through the global market economy. J Environ Manage 2016;183:959–71. [8] Zhang C, Li B, Rao F, Li P, Li X. A shock tube study of the autoignition characteristics of RP-3 jet fuel. Proc Combust Inst 2015;35:3151–8. [9] Zhu Y, Li S, Davidson DF, Hanson RK. Ignition delay times of conventional and alternative fuels behind reflected shock waves. Proc Combust Inst 2015;35:241–8. [10] Wang H, Oehlschlaeger MA. Autoignition studies of conventional and FischerTropsch jet fuels. Fuel 2012;98:249–58. [11] Shrestha A, Zheng Z, Badawy T, Henein N, Schihl P. Development of JP-8 surrogates and their validation using ignition quality tester. SAE Int J Fuels Lubricants: SAE
9