Pilot Injection Strategy Research Articles

Reduced Order Modeling of Engine Transients for Gasoline Compression Ignition Combustion Control

<div class="section abstract"><div class="htmlview paragraph">This work focuses on reducing the computational effort of a 0-dimensional combustion model developed for compression ignition engines operating on gasoline-like fuels. As in-cylinder stratification significantly contributes to the ignition delay, which in turn substantially influences the entire gasoline compression ignition combustion process, previous modeling efforts relied on the results of a 1-dimensional spray model to estimate the in-cylinder fuel stratification. Insights obtained from the detailed spray model are leveraged within this approach and applied to a reduced order model describing the spray propagation. Using this computationally efficient combustion model showed a reduction in simulation time by three orders of magnitude for an entire engine cycle over the combustion model with the 1-dimensional spray model. Capturing only the basic features of the spray propagation did not show a substantial decrease in prediction accuracy compared to the 1-dimensional spray model proposed in a previous publication. The reduced order model is able to predict CA50 within ±1CAD for most conditions. Having an estimate of the heat release within the engine as a function of various parameters, combined with first-order transfer functions reflecting the intake dynamics of the engine, allows using this as a full engine model suitable for transient engine simulations. These intake gas dynamics were obtained by applying step changes to engine parameters of interest. From a controls perspective, this engine model is utilized as a plant in a control system to simulate the closed-loop response based on various changes in input parameters. Engine responses and control actions for reference tracking in combustion phasing were investigated for early as well as late pilot injection strategies.</div></div>

Influence of aging of a diesel injector on multiple injection strategies

Multiple injection strategies have contributed to the improvement of thermal processes in Internal Combustion Engines. On this matter, the correct performance of the injector is a critical factor in the implementation of these techniques, as changes in the behavior of the injector could affect the injection development, altering the combustion process and heat transformation efficiency. Thus, the present study analyzes the development of multiple injection events in a diesel injector aged due to partial obstruction of the holes of the nozzle. To this end, a multi-hole piezoelectric injector was employed, in which the aging of the injector is evaluated through momentum flux measurements for each hole. Afterwards, rate of injection tests with pilot and post injection strategies are performed, and the results are compared to the injection events made by the same injector before aging. The results provided by the momentum flux experiments confirmed the partial obstruction of two holes. Furthermore, rate of injection comparisons showed that the injector had a lower steady-state rate of injection after aging and required a longer time to end the injection. These phenomena affected the multiple injection events, as the extended time required to end the injection reduced the hydraulic dwell time between pilot/post injection and the main injection. Furthermore, for short dwell times, this phenomenon led to the unification of the main and post injection, resulting in a large single injection. Hence, not only an increase in fuel consumption would appear, but the thermal benefits of implementing the post injection would be lost.

Analysis of the effects of multiple injection strategies with hydrogen on engine performance and emissions in diesel engine

In this study, firstly, the turbocharged, compression-ignition, light duty vehicle engine was loaded with a DC dynamometer. The real test engine was run at partial load (90%) and at different engine speeds with normal diesel fuel. In the second stage, a model engine was created and verified with the mixing control combustion (MCC) module suitable for hydrogen combustion using AVL BOOST simulation software with real test parameters such as engine performance and cylinder pressure values. At the last stage, multiple hydrogen injection strategies were applied in the simulation program using pure hydrogen as pilot and post fuel and diesel as the main fuel, and were examined numerically in terms of performance and emissions. The results showed that 2 pilot injections and 1 post-injection strategy reduced soot emissions more than 1 pilot injection strategy. However, NOx increased slightly in all three injection applications. In addition, a significant increase in engine power was observed.

CFD Simulation of a DME Fuelled CI Engine

A computational study is conducted for a DME fuelled CI engine of 373.3 cm3 displacement and 17.8 compression ratio at moderate load with detailed chemistry. Due to the symmetry of the cylinder, the simulations are conducted on a sector of the cylinder, from the closing of intake valve to the opening of exhaust valve. In the pilot injection strategy employed, 10% of the total fuel is injected during the pilot injection and the balance in the main injection at 50 BTDC. The computational model is first validated using the experimental data. Results show two-stage ignition characteristic for the DME injected in the pilot injection.

Effect of isopropanol and n-pentanol addition in diesel on the combustion and emission of a common rail diesel engine under pilot plus main injection strategy

In this study, isopropanol and n-pentanol are blended in diesel with 20% ratio by volume, named D80IP20 and D80NP20. Their combustion and emission performances were compared with diesel on a four cylinder common rail diesel engine under pilot plus main injection strategy. The pilot injection duration decreases and the main injection duration increases with engine loads. For test fuels, the starts of pilot and main injection and the durations of pilot injection are remained unchanged in each engine operation. D80IP20 has the longest ignition delay due to the lowest cetane number and the shortest combustion duration due to the highest fuel oxygen. However, the peak combustion temperature of D80IP20 is lower than that of D80NP20 under double injection strategy. Compared to diesel, both D80IP20 and D80NP20 obviously reduce the particle number concentrations (PNCs) and the particle volume concentrations (PVCs), while increase the NOx emissions. D80IP20 has the lowest PNCs and PVCs and its number geometric mean diameter (NGMD) and volume geometric mean diameter (VGMD) are the lowest among the three fuels. D80IP20 has higher NOx emission than diesel, but lower than D80NP20 due to lower PCT. Further, D80IP20 with 10% EGR can achieve the simultaneous reduction for NOx emission and PNCs at low and high loads compared to diesel without EGR. Results indicate that blending isopropanol in diesel has better effects in combustion improvement and emission control and is more suitable than n-pentanol under pilot plus main injection strategy.

Fuel Injection Strategy for Utilization of Mineral Diesel-Methanol Blend in a Common Rail Direct Injection Engine

AbstractMethanol fueled internal combustion (IC) engines have attracted significant attention due to their contributions in reducing environmental pollution and fossil fuel consumption. In this study, a single-cylinder research engine was operated on MD10 (10% (v/v) methanol blended with mineral diesel) and baseline mineral diesel to explore an optimized fuel injection strategy for efficient combustion and reduced emissions. The experiments were conducted at constant engine speed (1500 rpm) and load (3 kW) using two different fuel injection strategies, namely, single pilot injection (SPI) and double pilot injection (DPI) strategy. For each pilot fuel injection strategy, the start of main injection (SoMI) timing was varied from −3 to 6° crank angle (CA) before top dead center (bTDC). To examine the effect of fuel injection pressure (FIP), experiments were performed at three different FIPs (500, 750, and 1000 bars). Results showed that the MD10 fueled engine resulted in superior combustion compared with baseline mineral diesel, which was further improved by DPI at higher FIPs. The use of DPI strategy was found to be more effective at higher FIPs, resulting in higher brake thermal efficiency (BTE), lower exhaust gas temperature (EGT), and reduced oxides of nitrogen (NOx) emissions compared with SPI strategy. Detailed investigations showed that the addition of methanol in mineral diesel reduced particulates, especially the accumulation mode particles (AMP). Different statistical analysis and qualitative correlations between fuel injection parameters showed that higher FIP and advanced SoMI timings were suitable for particulate reduction from the MD10 fueled engine.

Study of using diesel/high-ON biofuel blends as the pilot fuel with large proportion and split injection in the dual-fuel combustion

Dual-fuel combustion using diesel and high-octane number (ON) biofuel of n-butanol blends to ignite compressed natural gas (CNG) with pilot fuel split injection was investigated. 30% n-butanol/70% diesel (B30D70) and pure diesel (B0D100) as the pilot fuels were compared with the start of pre-injection (SOIp) timings swept from −30 (SOIp30) to −80 °CA ATDC (SOIp80) under the CNG substitution rates of 50% at low load and 65% at medium load. A fixed start of main-injection (SOIm) timing of −9 °CA ATDC in B0D100 and various SOIm timings in B30D70 to match CA50 of B0D100 were employed. The experimental results indicated that adding n-butanol in the pilot fuel can significantly reduce the PM emission at advanced SOIp timings even with large proportion of pilot fuel. At low load, B30D70 reveals higher indicated thermal efficiency (ITE) due to its shorter combustion duration compared to B0D100, and it also leads to lower NOx emissions resulted from the more homogeneous mixture. The CO and THC emissions tend to be slightly increased in B30D70 for the advanced SOIp timings. At medium load, B30D70 also obtains higher ITE but yields higher NOx emissions. Relatively low level of NOx emissions can be obtained at early SOIp timings, such as SOIp60, SOIp70 and SOIp80. The CO and THC emissions are similar for the two pilot fuels at these timings. For the comparisons of the two pilot fuels and injection strategies, it can be demonstrated that B30D70 is more favorable to the thermal efficiency and emissions with split injection at SOIp40 under low load condition and early SOIp timings under medium load condition.

Suppression of instabilities of swirled premixed flames with minimal secondary hydrogen injection

The impact of hydrogen addition on the dynamics of a methane-air premixed flame is explored for different injection strategies. The configuration is a swirled injector with a central tube for pilot fuel injection. Keeping the air flow rate and thermal power of the burner constant, it is shown that even for very small flow rates of hydrogen, as low as one percent of the thermal power, flame stabilization and combustor stability are greatly altered when pure hydrogen is injected through the central tube as a pilot jet. It is also shown that fully premixing the same quantity of hydrogen with methane or use of methane for the pilot jet has no significant effects compared to hydrogen pilot injection strategy. The flame response to forced flow perturbations is use to interpret the observed features. It is shown that hydrogen piloting drastically changes the gain of the flame transfer function at low frequencies and its phase lag at high frequencies, while other injection strategies barely change the flame response for these minute flowrates. CO and NOx emissions are finally examined for the different injection strategies. NOx emissions are found to drastically increase with hydrogen piloting compared to other injection strategies. These experiments indicate that pure hydrogen injected in minute fractions may be used as an efficient passive control means to mitigate combustion instabilities, but a compromise needs to be made with emissions.

Analysis on the effect of pilot injection strategies on combustion and emission characteristics of palm-munja biodiesel/diesel blend on CRDI diesel engine

Multiple injection strategy is a vital strategy to reduce the soot and NO x emissions concurrently. The multiple injection strategy can enhance the air/fuel mixture, combustion and exhaust emission characteristics by providing a small amount of fuel before the main injection. Among all types of alternate fuels, biodiesel has emerged as an eco-friendly fuel for the diesel engines. This paper is focusing on the effect of pilot injection strategies on diesel engine say timing (−30° bTDC to −50° bTDC) and by varying the fuel quantity (5–15%). The performance, combustion and emission characteristics of Palm-munja biodiesel/diesel blend (B20) were investigated on CRDI diesel engine. The experimentations were carried out on a constant speed by varying loads from 0 to 100%. The experimental results show that as an increase in pilot injection timing there is a reduction in the in-cylinder pressure, whereas soot and NO x emissions decrease as the pilot injection timing increases. As the pilot injection fuel quantity increases, the in-cylinder pressure and NO x emission increase, whereas soot emission decreases.

Assessment of pilot injection strategies and n-pentanol additive effects on engine performance and emissions

Biodiesel is a environmentally friendly, biodegradable and renewable alternative fuel, which is widely used around the world. However, the higher viscosity and NOX emissions are its main drawbacks. n-Pentanol has lower viscosity, higher oxygen content and volatility as compared with biodiesel, which is a promising additive for biodiesel/diesel blends. In this work, the influences of pilot injection (PI) strategies included pilot-main interval (PMI) and pilot injection rate (PIR), and n-pentanol additive on emission characteristics and combustion behaviors of a diesel engine at medium load were investigated. The three test fuels including diesel (D100), a mixture of 20% biodiesel and 80% diesel (BD20), and 20% n-pentanol, 16% biodiesel and 64% diesel (BDP20), respectively. The results indicated that, compared with single injection (SI), the peak of main injection heat release rate reduced and brake thermal efficiency (BTE) increased when using PI strategies. Adding n-pentanol to biodiesel/diesel (BD) blends resulted in an increase in maximum in-cylinder pressure, but BTE decreased. After utilizing PI strategies, the NOX emissions decreased significantly, but the soot, CO and THC emissions increased. As the PIR and PMI increased, the accumulation mode particles and total particle mass concentrations increased. Compared with SI, the ratio of sub-25 nm particles of BDP20 decreased with the use of PI strategies. The combination of n-pentanol additive and small PMI strategies could achieve lower total particles number concentration and smaller geometric mean diameter when compared with pure diesel.

Experimental investigation of pilot-fuel combustion in dual-fuel engines, Part 1: Thermodynamic analysis of combustion phenomena

The pilot-fuel auto-ignition and combustion in compressed methane/air mixtures are investigated. Experiments were performed in an optically accessible rapid compression-expansion machine featuring quiescent charge conditions and a single-hole coaxial diesel injector mounted on the cylinder periphery. It enabled thermodynamic analysis of the pilot-fuel combustion without these phenomena being masked by the rapid premixed-flame propagation like in the engine test rigs with turbulent charge. The aim of this study is to elucidate the first-order influences of charge and pilot-fuel parameters on the ignition delay and transition into the premixed flame propagation. For this purpose, a comprehensive measurement matrix including variations of the premixed fuel equivalence ratio, charge temperature, and oxygen content as well as the variation of pilot injection duration is tested. The heat release rate (HRR) metrics describing the pilot-fuel combustion duration, peak HRR, and cumulative HRR during the pilot-fuel combustion are derived. Correlations of the HRR metrics to the ignition delay, pilot-fuel mixing state at ignition and the volume of the pilot-fuel jet are investigated. Methane is found to increase the ignition delay and prolong the pilot-fuel combustion duration. This effect is amplified for pilot-injection strategies with leaner pilot-fuel mixtures at ignition or in the case of reduced charge oxygen content. Despite the reduced pilot-fuel reactivity the co-combustion of entrained methane leads to higher peak-HRR, except in the reduced charge oxygen cases, where the excessively reduced mixture reactivity with the introduction of methane leads even to a reduced peak-HRR.The phenomenology of the dual-fuel combustion process is described in Part 1, whereas Part 2 of this work aims at improving the understanding of the underlying processes by application of advanced optical diagnostic methods.

Effects of pine oil additive and pilot injection strategies on energy distribution, combustion and emissions in a diesel engine at low-load condition

Pine oil is mainly produced from the pine tree, which has some prominent fuel-related properties, such as lower boiling point and viscosity than those of the pure diesel. Particularly, its low heating value is similar to that of diesel. In addition, pine oil and diesel can be mixed in any ratio, and the engine can directly burn the pine oil/diesel mixtures without any further modification. Therefore, pine oil is considered to be a promising additive to diesel fuel. However, when pine oil is fueled in a diesel engine via single injection the engine NOX emissions deteriorate. In this present study, the effects of pilot injection (PI) strategies, including pilot injection rate (PIR) and pilot-main interval (PMI) on energy distribution, emissions and combustion were explored in a diesel engine fueling with diesel/pine oil mixtures at low-load condition. Three test fuels were pure diesel (denoted as P0), a mixture of 80% diesel and 20% pine oil (denoted as P20), and 60% diesel and 40% pine oil (denoted as P40), respectively. The results showed that, after utilizing the PI strategies, the peaks of in-cylinder pressure of the three fuels increased compared to single injection, while the maximum pressure rise rates decreased along with an increase in the break thermal efficiency (BTE). After blending pine oil in pure diesel, both the soot and CO emissions were reduced, although the NOX and THC emissions slightly increased. The small PMI strategies could reduce the energy loss of THC, CO emissions and friction, and improve BTE. However, the soot emission increased. At low-load condition, when fueling with P20 blended fuel and using small PMI strategies, the system could achieve higher thermal efficiency and lower soot-NOX emissions than the strategy employing pure diesel.

Mechanism of Combustion Noise Influenced by Pilot Injection in PPCI Diesel Engines

Pilot injection combined with exhaust gas recirculation (EGR) is usually utilized to realize the partially premixed compression ignition (PPCI) mode in diesel engines, which enables the simultaneous decrease of nitrogen oxide and soot emissions to satisfy emission regulations. Moreover, the ignition delay of main injection combustion can also be shortened by pilot injection, and then combustion noise is reduced. Nevertheless, the mechanisms of pilot injection impacts on combustion noise are not completely understood. As such, it is hard to optimize pilot injection parameters to minimize combustion noise. Therefore, experiments were conducted on a four-stroke single-cylinder diesel engine with different pilot injection strategies and 20% EGR as part of an investigation into this relationship. Firstly, the combustion noise was analyzed by cylinder pressure levels (CPLs). Then, the stationary wavelet transforms (SWTs) and stationary wavelet packet transform (SWPT) were employed to decompose in-cylinder pressures at different scales, and thus the combustion noise generated by pilot and main combustion was investigated in both the time and frequency domain. The results show that pilot injection is dominant in the high frequency segment of combustion noise, and main injection has a major impact on combustion noise in the low and mid frequency segment. Finally, the effects of various pilot injection parameters on suppressing combustion noise were analyzed in detail.

Numerical Study on the Effects of Multiple-Injection Coupled with EGR on Combustion and NOx Emissions in a Marine Diesel Engine

In this work, the potential of multi-injection strategies coupled with EGR to improve the trade-off relationship of NOx-BSFC (Brake specific fuel consumption) is carefully studied by multi-dimensional simulation using CONVERGE in a low-speed two-stroke diesel engine. The present study reveals that by introducing high EGR rate, the reduction of NOx emissions, the peak heat release rate and the peak pressure can be observed. But the effective fuel consumption rate is increased. We investigate the effects of various multiple-injection strategies on the engine performance, that is, single pilot-injection, single post-injection, single pilot-injection combined with single post-injection, and double pilot-injections, coupled with 39% EGR. The results show that low BSFC can be effectively achieved by a single pilot-injection strategy of small interval and large quantity. However, with a comprehensive consideration of low NOx emissions and BSFC, a strategy of 25 °CA pilot-main interval and 20% quantity should be chosen to obtain the best performance. The analysis of post-injection reveals that it is beneficial to reducing NOx emissions, but BSFC can be deteriorated. Moreover, it can be concluded that it is possible to achieve low NOx emissions and fuel consumption simultaneously by using the pilot-injection combined with post-injection. It also can be found that NOx emissions are deteriorated remarkably when using double pilot-injections.

N-Butanol reactivity modulation with early fuel injections for low NOx compression ignition combustion

This paper investigates pilot injection strategies to improve the combustion controllability of a premixed n-butanol cylinder charge while achieving ultra-low NOx emissions comparable to homogenous charge compression ignition (HCCI). Detailed insights are given for the ignition processes controlled by fuel and reactivity stratification. The n-butanol port injection is applied to form a homogeneous cylinder charge, an early pilot direct injection of either n-butanol or diesel is generated to control the ignition and combustion. In dual-fuel reactivity stratification combustion (RSC) strategy with an early diesel pilot injection, the prompt control of combustion phasing relies on fuel energy ratio adjustment. Under heavy EGR, the RSC can lower the NOx emissions to the level of 10 ppm and retain the combustion completeness, however, at the cost of increased pressure rise rate. EGR plays a key role in suppressing the pressure rise rate for load extension of RSC combustion. In order to maintain a moderate pressure rise rate when the engine load increases, the combustion phasing must be retarded through heavy EGR together with increased PFI n-butanol energy ratio, which leads to an efficiency penalty. In the single-fuel strategy, the early pilot injection of n-butanol results in fuel stratification in the cylinder which is responsible for the combustion initiation. The single-fuel strategy retains effective ignition controllability although the start of combustion manifests less sensitivity to the n-butanol pilot injection timing. In the tested low to medium engine load range, the single-fuel strategy can achieve NOx emissions level same to HCCI combustion, while the NOx emissions of dual-fuel RSC strategy are slightly higher because of the reactivity gradient and more advanced combustion phasing.

The impact of water injection and exhaust gas recirculation on combustion and emissions in a heavy-duty compression ignition engine operated on diesel and gasoline

Steady-state experiments were conducted on a 12.4L, six-cylinder heavy-duty engine to investigate the influence of port-injected water and dilution via exhaust gas recirculation (EGR) on combustion and emissions for diesel and gasoline operation. Adding a diluent to the combustion process reduces peak combustion temperatures and can reduce the reactivity of the charge, thereby increasing the ignition-delay and, allowing for more time to premix air and fuel. Experiments spanned water/fuel mass ratios up to 140mass% and exhaust gas recirculation ratios up to 20vol% for gasoline and diesel operation with different injection strategies. Diluting the combustion process with either water or EGR resulted in a significant reduction in nitrogen oxide emissions along with a reduction in brake thermal efficiency. The sensitivity of brake thermal efficiency to water and EGR varied among the fuels and injection strategies investigated. An efficiency breakdown revealed that water injection considerably reduced the wall heat transfer; however, a substantial increase in exhaust enthalpy offset the reduction in wall heat transfer and led to a reduction in brake thermal efficiency. Regular diesel operation with main and post injection exhibited a brake thermal efficiency of 45.8% and a 0.3% reduction at a water/fuel ratio of 120%. The engine operation with gasoline, early pilot, and main injection strategy showed a brake thermal efficiency of 45.0% at 0% water/fuel ratio, and a 1.2% decrease in brake thermal efficiency for a water/fuel ratio of 140%. Using EGR as a diluent reduced the brake thermal efficiency by 0.3% for diesel operation, comparing ratios of 0% and 20% EGR. However, a higher impact on brake thermal efficiency was seen for gasoline operation with early pilot and main injection strategy, with a reduction of about 0.8% comparing 0% and 20% EGR. Dilution by means of EGR exhibited a reduction in nitrogen oxide emissions up to 15 g/kWh; water injection showed only up to 10 g/kWh reduction for the EGR rates and water/fuel ratio investigated.

Influence of n-butanol-diesel-PODE3-4 fuels coupled pilot injection strategy on combustion and emission characteristics of diesel engine

Experiments in regard to influence of n-butanol, diesel and PODE3-4 hybrid fuel coupled pre-injection strategy on combustion and emission characteristics of diesel engine were conducted at 20% EGR (exhaust gas recirculation) rates. BD20 that composed of 20% n-butanol and 80% conventional diesel (v/v), PD20 that composed of 20% PODE3-4 and 80% conventional diesel (v/v), BDP20 that composed of 20% PODE3-4 and 80% BD20 (v/v), and pure diesel fuel (D100) were tested. The results showed that compared to a single injection route, pilot injection route lowers the MPRR (Maximum Pressure Rise Rate). By decreasing pilot injection interval or increasing the pilot injection rate, MPRR is further reduced. MPRR can be reduced by blending PODE3-4, and the descending sequence of MPRR for the four fuels is: BD20 > BDP20 > D100 > PD20. Moreover, adding the oxygenated fuel into diesel causes the NOx emission increase, and the change of pilot injection strategy impacts little on NOx emission of all the four fuels. The descending sequence of soot emission is: D100 > BD20 > PD20 > BDP20, where soot emission of D100 increases as pilot injection rate increases or decreases due to the increases of pilot injection interval, while emissions of other remaining three blends are insensitive to pilot injection strategy. The accretion of PODE3-4 in the D100 or BD20 shows a significant downtrend in CO emission, where that of BDP20 is the lowest; CO and HC emissions of the four fuels increase due to the increases of pilot injection interval, and enhancing the pilot rate results in reduction in HC emissions of PD20 and BDP20, but the change of CO emission is not obvious. By introducing the pilot injection, the total particle number concentration of pure diesel increases, but with modest effect on those of the blends. Regardless of single injection or pilot injection, total particle number concentrations of multi-fuels are significantly lowered compared with that of D100.

Comparative study on single-injection and pilot-injection strategies for DI CI engine fuelled with the butanol/diesel blend

ABSTRACT The present paper discusses a comparative study of single- and pilot-injection strategy fuelled with diesel (i.e. Bu00) and 15% of butanol blend (i.e. Bu15). The effects of pilot injection timing (−33° bTDC to −73° bTDC) and pilot injection fuel quantity (5–20%) with 15% of butanol blend were carried out numerically using CONVERGE CFD Code. The results show that in single-injection strategy, NOx, CO and soot emissions reduce, whereas UBHC emission increases with the addition of butanol content. In pilot-injection strategy, when the first fuel injection timing is advanced, the peak value of heat release rate (HRR) for the first injected fuel reduces, but marginally improves for the main injected fuel. Increasing the first injection fuel quantity, the HRR of the peak value for first injected fuel increases but the HRR of the peak value for second injected fuel reduces. Minimum ISFC was obtained at 10% of pilot injection fuel quantity and −53° bTDC of pilot injection timing.

Effects of pilot injection strategy of diesel fuel on combustion characteristics in a premixed methanol-air mixture atmosphere in a CVCC

The experimental research on effects of diesel pilot injection strategy, including pilot injection timing (t2) and mass (mdp), on the combustion of diesel in a premixed methanol-air mixture atmosphere were conducted in a newly developed constant volume combustion chamber (CVCC), where both methanol and diesel fuel were injected directly into the chamber. Results showed that pilot injection makes the ignition of main injection advance; ignition position move towards the nozzle tip; and the natural flame luminosity become stronger. In diesel/methanol dual fuel mode (DM), the wrinkles on the flame surface are more complicated and the area of natural flame luminosity is larger, especially in earlier t2 or more mdp conditions. Pilot injection shortens ignition delay and ignition delay in DM is longer than that in diesel fuel mode (D). But when the interval between pilot and main injection (Δt2) is longer than 2 ms or mdp is more than 3.28 mg, ignition delay in DM becomes shorter instead. In D the changes of Δt2 and mdp have no significant effects on flame lift-off length (FLoL). But FLoL shortens gradually with the advance of t2 and the increase of mdp in DM. After adding pilot injection, the start of spatially integrated natural luminosity (SINL) rising advances and SINL peak increases. TINL in DM is lower than that in D. But when Δt2 is longer than 2 ms or mdp is more than 3.28 mg, TINL in DM becomes higher instead. Pilot injection can change heat release rate (HRR) from bimodal to unimodal and reduce the HRR peak of main combustion simultaneously.

Effects of Triple Injection Strategies on Performance and Pollutant Emissions of a DI Diesel Engine Using CFD Simulation

One of the main controlling parameters in diesel engine combustion is the fuel – air mixing process that has direct effects on engine performance and pollutant emissions, reviewing over previous literature showed that split injection strategies could satisfy this purpose very well. For the first time and in this paper, pilot and double injection strategies were combined and formed new triple injection strategy that has not been considered by any other researchers. In this study after achieving successful validation between modeling and experimental results for both single and double injection strategies, optimization of triple injection strategy was conducted, in which first pulse of double injection strategy divided in to two pulses, then amount of injected fuel in each pulse kept constant and different delay times between first and second pulse of injections were investigated. For better understanding the processes the injections were done inside the engine, diagrams of heat release rate, in cylinder temperature, in cylinder pressure, NOx and soot emissions were presented. Results showed that decreasing the delay time between second and third pulse of injections could decrease the ratio of premixed combustion of third pulse and in optimum cases, reduction in both NOx and soot emissions could be achieved in comparition with single and double injection strategies, without any significant effects on engine performance. Furthermore, triple injection strategy with second pulse of injection that started at 4 crank angle before top dead center was selected to be the optimum case in reduction of both emissions.