Pilot Injection Timing Research Articles

Effects of Pilot Injection Timing and EGR on Combustion, Performance and Exhaust Emissions in a Common Rail Diesel Engine Fueled with a Canola Oil Biodiesel-Diesel Blend

Biodiesel as a clean energy source could reduce environmental pollution compared to fossil fuel, so it is becoming increasingly important. In this study, we investigated the effects of different pilot injection timings from before top dead center (BTDC) and exhaust gas recirculation (EGR) on combustion, engine performance, and exhaust emission characteristics in a common rail diesel engine fueled with canola oil biodiesel-diesel (BD) blend. The pilot injection timing and EGR rate were changed at an engine speed of 2000 rpm fueled with BD20 (20 vol % canola oil and 80 vol % diesel fuel blend). As the injection timing advanced, the combustion pressure, brake specific fuel consumption (BSFC), and peak combustion pressure (Pmax) changed slightly. Carbon monoxide (CO) and particulate matter (PM) emissions clearly decreased at BTDC 20° compared with BTDC 5°, but nitrogen oxide (NOx) emissions increased slightly. With an increasing EGR rate, the combustion pressure and indicated mean effective pressure (IMEP) decreased slightly at BTDC 20° compared to other injection timings. However, the Pmax showed a remarkable decrease. The BSFC and PM emissions increased slightly, but the NOx emission decreased considerably.

Ethanol-fueled low temperature combustion: A pathway to clean and efficient diesel engine cycles

Low temperature combustion (LTC) in diesel engines offers the benefits of ultra-low NOx and smoke emissions but suffers from lowered energy efficiency due to the high reactivity and low volatility of diesel fuel. Ethanol from renewable biomass provides a viable alternate to the petroleum based transportation fuels. The high resistance to auto-ignition (low reactivity) and its high volatility make ethanol a suitable fuel for low temperature combustion (LTC) in compression-ignition engines.In this work, a Premixed Pilot Assisted Combustion (PPAC) strategy comprising of the port fuel injection of ethanol, ignited with a single diesel pilot injection near the top dead centre has been investigated on a single-cylinder high compression ratio diesel engine. The impact of the diesel pilot injection timing, ethanol to diesel quantity ratio and exhaust gas recirculation on the emissions and efficiency are studied at 10 bar IMEP. With the lessons learnt, successful ethanol–diesel PPAC has been demonstrated up to a load of 18bar IMEP with ultra-low NOx and soot emissions across the full load range. The main challenge of PPAC is the reduced combustion efficiency especially at low loads; therefore, the authors have presented a combustion control strategy to allow high efficiency, clean combustion across the load range. This work entails to provide a detailed framework for the ethanol-fueled PPAC to be successfully implemented.

Experimental investigations of the effect of pilot injection on performance, emissions and combustion characteristics of Karanja biodiesel fuelled CRDI engine

Pilot and post injections are being used in modern diesel engines for improving engine performance in addition to meeting stringent emission norms. Biodiesel produced from different feedstocks is gaining global recognition as partial replacement for mineral diesel in compression ignition (CI) engines. In this study, 10%, 20% and 50% Karanja biodiesel blends were used for investigation of pilot injections, injection pressures and injection timings on biodiesel blends. Experiments were carried out in a single cylinder CRDI research engine in multiple injection mode at 500 and 1000 bar fuel injection pressure (FIP) under varying start of pilot injection (SOPI) and start of main injection (SOMI) timings. Brake specific fuel consumption (BSFC) increased with increasing Karanja biodiesel concentration in test fuels however brake thermal efficiency (BTE) of biodiesel blends was slightly higher than mineral diesel. Lower biodiesel blends showed lower brake specific carbon monoxide (BSCO) and brake specific hydrocarbon (BSHC) emissions than mineral diesel. Brake specific nitrogen oxides (BSNOx) emissions from KOME20 and KOME10 were higher than mineral diesel. Combustion duration of KOME50 was also higher than mineral diesel.

Parametric investigation of natural gas port injection and diesel pilot injection on the combustion and emissions of a turbocharged common rail dual-fuel engine at low load

In this paper, a common rail diesel research engine was converted to operate in dual-fuel mode and extensive experiments were conducted to investigate the effects of natural gas injection timing on the combustion and emissions performance under different pilot injection pressure and timing at low load conditions. The presented results include the cylinder pressure, heat release rate (HRR), ignition delay, combustion duration and brake thermal efficiency, as well as CO, HC and NOx emissions at different natural gas injection timing under pilot injection pressure (46 and 72MPa) and pilot injection timing (−8° and −17° ATDC) operation conditions at low load (BMEP=0.24MPa). The results indicated that retarded natural gas injection timing can achieve a stratified-like air–fuel mixture in cylinder under the different pilot injection conditions, which provided a method to improve the combustion performance and exhaust emissions at low load. Moreover, under higher pilot injection pressure (72MPa) conditions, better combustion performance, such as shorter ignition delay and combustion duration, higher brake thermal efficiency, were achieved; however, the exhaust emissions significantly increased compared with those under lower pilot injection pressure (46MPa). On the other hand, under the advanced pilot injection timing (−17° ATDC), the combustion performance was radically better, THC and CO emissions were lower but the NOx emissions were significantly higher compared with those under the regular pilot injection timing (−8° ATDC). This is attributed to faster flame propagation speed, better combustion phasing and higher volumetric efficiency. Consequently, employing appropriate natural gas injection timing accompanied with reasonable pilot injection parameters is critical to further improve combustion performance and exhaust emissions of a dual-fuel engine at low loads.

Effect of Premixed Fuel Preparation for Partially Premixed Combustion With a Low Octane Gasoline on a Light-Duty Multicylinder Compression Ignition Engine

Gasoline compression ignition (GCI) concepts with the majority of the fuel being introduced early in the cycle are known as partially premixed combustion (PPC). Previous research on single- and multicylinder engines has shown that PPC has the potential for high thermal efficiency with low NOx and soot emissions. A variety of fuel injection strategies have been proposed in the literature. These injection strategies aim to create a partially stratified charge to simultaneously reduce NOx and soot emissions while maintaining some level of control over the combustion process through the fuel delivery system. The impact of the direct injection (DI) strategy to create a premixed charge of fuel and air has not previously been explored, and its impact on engine efficiency and emissions is not well understood. This paper explores the effect of sweeping the direct injected pilot timing from −91 deg to −324 deg ATDC, which is just after the exhaust valve closes (EVCs) for the engine used in this study. During the sweep, the pilot injection consistently contained 65% of the total fuel (based on command duration ratio), and the main injection timing was adjusted slightly to maintain combustion phasing near top dead center. A modern four cylinder, 1.9 l diesel engine with a variable geometry turbocharger (VGT), high pressure common rail injection system, wide included angle injectors, and variable swirl actuations was used in this study. The pistons were modified to an open bowl configuration suitable for highly premixed combustion modes. The stock diesel injection system was unmodified, and the gasoline fuel was doped with a lubricity additive to protect the high pressure fuel pump and the injectors. The study was conducted at a fixed speed/load condition of 2000 rpm and 4.0 bar brake mean effective pressure (BMEP). The pilot injection timing sweep was conducted at different intake manifold pressures, swirl levels, and fuel injection pressures. The gasoline used in this study has relatively high fuel reactivity with a research octane number of 68. The results of this experimental campaign indicate that the highest brake thermal efficiency (BTE) and lowest emissions are achieved simultaneously with the earliest pilot injection timings (i.e., during the intake stroke).

Optimization of EGR and split injection strategy for light vehicle diesel low temperature combustion

Low temperature combustion was developed using a four-cylinder light vehicle diesel engine. Operating conditions considered were 1600 rpm, 1bar and 3bar IMEP. Both EGR and split injection strategy were optimized in order to obtain the lowest BSFC accompanied with a low level of emissions. It was found that a late injection strategy with high levels of EGR rate was required for simultaneous reduction of NOx and soot. However, the fuel consumption remains higher than the conventional combustion regime. Thus, the optimization study of injection parameters to improve the trade-off between NOx and soot emissions while maintaining good fuel efficiency was performed. Several injection pressures were tested. The results showed that as injection pressure increased, NOx emissions increased slightly, soot initially decreased sharply, but further increase of injection pressure on soot was not obvious at low temperature atmosphere, and might lead to increased BSFC. Next, split injection strategy was adopted, optimized pilot injection conditions for minimizing fuel consumption were found at late pilot injection timing with big injection quantity, but little amount of pilot injection could make better comprehensive performance of diesel engine. Through multi-parameter collaborative optimization, the emission reduction path was proposed at operating condition of partial load. Low NOx and soot emissions could be obtained with slightly increase of fuel consumption.

Effect of Pilot Injection Timings on the Combustion Temperature Distribution in a Single-Cylinder CI Engine Fueled with DME and ULSD

Many studies of DiMethyl Ether (DME) as an alternative fuel in Compression-Ignition (CI) engines have been performed. Although diverse DME engine research has been conducted, the investigation of combustion behavior and temperature distribution in the combustion engine has not progressed due to the fact that there is no sooting flame in DME combustion. In order to investigate the combustion characteristics in this study, the KIVA-3 V code was implemented to research various pilot injection strategies on a single-cylinder CI engines with DME and Ultra-Low-Sulfur Diesel (ULSD) fuels. The combustion distribution results obtained from the numerical investigation were validated when compared with the measurement of flame temperature behaviors in the experimental approach.This study showed that long intervals between two injection timings enhanced pilot combustion by increasing the ambient pressure and temperature before the start of the main combustion. Different atomization properties between DME and ULSD fuels contributed to the formation of a fuel-air mixture at the nozzle tip and piston lip regions, separately, which strongly affected the temperature distribution of the two fuels. In addition, the pilot injection timing played a vital role in regard to ignition delay and peak combustion temperatures. Exhaust emissions, such as NOx and soot, are related to the local equivalence ratio and temperature in the combustion chamber, also illustrated by the contrary result on a Φ (equivalence ratio) – T (temperature) map.

Study of Pilot Injection for the Improvement of Combustion and Emissions Characteristics in a Heavy-Duty Diesel Engine

A 6-cylinder, turbocharged, common rail heavy-duty diesel engine was used in this study. The effect of pilot injection strategies on diesel fuel combustion process, heat release rate, emission and economy of diesel engine is studied. The pilot injection strategies include pilot injection timing and pilot injection mass to achieve the homogeneous compression ignition and lower temperature combustion of diesel engine. The two-color method was applied to take the flame images in the engine cylinder and obtain soot concentration distribution. The results demonstrate that with the advance of pilot injection timing, the peak in-cylinder pressure becomes lower, the ignition delay of the main combustion is shortened, the NOXand soot emissions are reduced, but the HC and CO emissions are increased. With the increase of pilot injection fuel mass, the heat release rate of the pilot injection combustion and the maximum rate of pressure rise increase, NOXand HC emissions are higher, and PM and CO emissions are reduced. The pilot combustion flame is non-luminous.

Experimental study of the effects of natural gas injection timing on the combustion performance and emissions of a turbocharged common rail dual-fuel engine

Natural gas combustion with pilot ignition has been considered to be one of the most promising ways to utilize natural gas in existing diesel engine without serious engine modification and it has been widely researched all over the world. In this study, three experiments of different loads (BMEP 0.240MPa, 0.480MPa and 0.767MPa) were performed on a 2.8L four-cylinder, natural gas manifold injection dual-fuel engine to investigate the effects of natural gas injection timing on engine combustion performance and emissions. The pilot injection parameters (pilot injection timing and pressure) and natural gas injection pressure remain constant at a speed of 1600rpm in the experiment. The cylinder pressure, HRR, CoVimep, flame development duration, CA50 and brake thermal efficiency were analyzed. The results indicated that under low and part engine loads, the flame development duration and CA50 can be reduced by properly retarding natural gas injection timing, while the CoVimep increased with retarded natural gas injection timing. As a result, the brake thermal efficiency is increased and the combustion stability slightly deteriorates. Meanwhile, under low and part engine loads, PM emissions in the dual-fuel engine is much lower than that in conventional diesel engines, furthermore, at high load, the PM emissions are near zero. CO and HC emissions are reduced with retarded natural gas injection timing under low and part loads, however, NOx emissions are slightly increased. Under high load, the flame development duration and CA50 are obviously prolonged with retarded natural gas injection timing companied with a deterioration of brake thermal efficiency. CO and HC emissions are not significantly varied with retarded natural gas injection timing under high load, except that NOx emissions decreased slightly.

바이오디젤 혼합 연료에 커먼레일 디젤기관에서 예비 분사시기가 연소 및 배기 특성에 미치는 영향

본 연구는 4실린더 커먼레일 디젤 기관에서 바이오 디젤 혼합 연료를 사용하여 예비 분사시기와 EGR율을 변화시켰을 때 연소 압력과 배기 특성에 미치는 영향을 조사하기 위하여 실험을 수행하였다. 예비 분사 시기와 EGR율은 디젤 기관의 연소 및 배기 배출 특성에 큰 영향을 미친다. 본 연구에서는 일반적으로 많이 사용되고 있는 기관 회전 속도 2,000rpm에서 바이오 디젤 혼합율 20%의 연료를 사용하여 예비 분사 시기와 EGR율에 다양하게 변화를 주어 실험을 하였다. 실험결과, 도시 평균 유효 압력은 예비 분사 시기가 상사점전 BTDC <TEX>$10^{\circ}$</TEX>에서 가장 높았으며, 연소 압력과 열 발생율은 동일 예비 분사 시기에서 EGR율에 비례하여 감소하였다. NOx배 출량은 예비 분사시기에 관계없이 EGR율이 증가할수록 큰 폭으로 감소하였으며, 매연(Soot)은 예비 분사 시기 BTDC <TEX>$20^{\circ}$</TEX>에서 가장 적게 배출되었다. An experimental study was performed to investigate the characteristics of combustion pressure and exhaust emissions when the pilot injection timing and EGR rate were changed in a CRDI 4-cylinder diesel engine using bio-diesel blended fuel. The pilot injection timing and EGR rate have a significant impact on the combustion and emission characteristics of diesel engine. In this study, the pilot injection timing and EGR rate variation were conducted to 2000rpm of engine speed with fuel of bio-diesel blended rate 20%. In these experimental results, IMEP was shown maximum pressure at pilot injection timing BTDC<TEX>$10^{\circ}$</TEX> combustion pressure and heat release rate were decreased in proportion to increase of EGR rate under the same pilot injection timing conditions. The NOx emission was decreased with increasing the EGR rate without influence on pilot injection timing. However, soot emission was reduced to a minimum at pilot injection timing BTDC<TEX>$20^{\circ}$</TEX>.

Investigating the relative contribution of operational parameters on performance and emissions of a common-rail diesel engine using neural network

Engine performance and emissions depend on a variety of parameters affecting the engine. Thanks to utilization of modern diesel engine with mechatronic systems, the number engine actuators increase significantly. The actuators can affect the internal states (operational parameters) of diesel engine such as inlet manifold pressure, EGR rate, quantity and timing of pilot and main injection which in turn will influence the engine emissions and performance. These internal states can be considered as boundary conditions of in-cylinder combustion process. Due to large number of effective parameters, study of relative contribution of these states on engine outputs will be helpful in better controlling and calibration of diesel engines. In this paper, comparative effects of internal states on both performance and emissions are investigated using statistical method and ranked based on their importance. Ten engine operational parameters including: injected fuel mass, pilot and main injection mass, main and pilot injection timing, inlet air pressure and temperature, exhaust pressure, fuel rail pressure and exhaust gas recirculation rate (EGR) are considered and their influence on brake torque, Soot, NOx and brake specific fuel consumption (BSFC) is investigated. A thermodynamic model of engine cycle is developed in AVL Boost®; the model is tuned and validated using experimental data. In order to better and faster study the effects of operational parameters on engine performance, a neural network is employed. The required data to train the neural networks is provided by using AVL Boost Design Explorer. Due to large number of inputs and outputs, a low-discrepancy and low-dispersion sequences generator called Sobol method is used to generate quasi random sequences of input data. More than 4000 engine operation points are generated and simulated in AVL Boost. The provided data is then used to train a feed forward neural network using Bayesian training method. Comparison between experimental data and simulated results shows about 6% error in prediction of the outputs. The engine performance and emission is then analyzed using both graphical and statistical methods to study how different input parameters can influence the engine emissions and performance. Finally, the relative importance of each parameter on different engine performance and emission characteristics are investigated using perturbation method and most influential parameters on different outputs are obtained.

An experimental study into the effect of the pilot injection timing on the performance and emissions of a high-speed common-rail dual-fuel engine

Dual-fuel technology has the potential to offer significant improvements in the emissions of carbon dioxide from light-duty compression ignition engines. In these smaller-capacity high-speed engines, where the combustion event can be temporally shorter, the injection timing can have an important effect on the performance and emissions characteristics of the engine. This paper discusses the use of a 0.51 l single-cylinder high-speed direct-injection diesel engine modified to achieve port directed gas injection. The effect of the pilot diesel injection timing on the dual-fuel engine performance and emissions was investigated at engine speeds of 1500 r/min and 2500 r/min and loads equivalent to gross indicated mean effective pressures of 0.15 MPa, 0.3 MPa, 0.45 MPa and 0.6 MPa, for a fixed gas substitution ratio (on an energy basis) of 50%. Furthermore, the effect of the pilot injection quantity was investigated at a constant engine speed of 1500 r/min by completing a gaseous substitution sweep at the optimised injection timing for each load condition. The results identify the limits of single-injection timing during dual-fuel combustion and the gains in the engine performance and stability that can be achieved through optimisation of the pilot injection timing. Furthermore, the pilot injection timing and quantity were shown to have fundamental effects on the formation and emissions of carbon monoxide, nitrogen oxide and total hydrocarbon. The potential for dual-fuel combustion to achieve significant reductions in the specific carbon dioxide was also highlighted, with reductions of up to 30% being achieved at full load compared with the baseline diesel case.

Combustion modelling for a diesel engine with multi-stage injection using a stochastic combustion model

This study presents the development of a phenomenological combustion model to simulate the combustion processes in diesel engines with multi-stage fuel injection. A newly developed zero-dimensional spray propagation model and a model of spray-to-spray interaction were combined with a stochastic combustion model, which had been developed for the calculation of diesel combustion in the case of single-stage injection. In this model, the combustion chamber is divided into an ambient air zone and several spray zones, where the spray formed by each injection is treated as a spray zone. The turbulent mixing, the fuel evaporation, the heat loss and the chemical reactions are calculated in each spray zone separately. A zero-dimensional spray propagation model including the spray evolution after the end of injection and a model of interaction between the sprays from sequential injections are developed to describe the spray behaviour for the case of multi-stage injection. Then the developed combustion model is validated against the experimental data from a single-cylinder direct-injection diesel engine with two-stage pilot–main injection, in which the pilot injection conditions are varied with a fixed main-injection timing. Based on the analysis of the heat release rate, the entrainment rate and the microscopic information inside the spray, such as the probability density function of the equivalence ratio, the effects of the wall impingement and the interaction between adjacent sprays on the fuel–air mixing rate and the entrainment rate are formularized and employed to reproduce the measured histories of the heat release rate. The reduction in the fuel–air mixing rate is considered when the spray flows into the squish region after wall impingement, which is effective in obtaining the measured decrease in the heat release of the pilot spray with advancing pilot injection timing. The effects of the wall impingement of the main spray and the interaction between adjacent sprays are modelled to reproduce the heat release rate during the initial part and later part of the mixing-controlled combustion. After these improvements, the heat release rates of the test engine when varying the pilot injection conditions were successfully predicted.

커먼레일식 디젤기관의 부분 예혼합 분사시기가 연소 및 배기특성에 미치는 영향

An experimental study was performed to investigate the characteristics of combustion pressure and exhaust emissions when the pilot injection timing and EGR rate were changed in a CRDI 4-cylinder diesel engine. The pilot injection timing and EGR rate have a significant impact on the combustion and emission characteristics of diesel engine. In this study, the pilot injection timing and EGR rate variation were conducted to 2000rpm of engine speed with torque 50Nm. Combustion pressure and heat release rate were decreased under high EGR rate conditions but increased under the pilot injection timing <TEX>$20^{\circ}$</TEX>(BTDC). IMEP and the maximum pressure in cylinder(Pmax) were decreased under the same injection timing with the increase of EGR rate. The NOx emission was decreased with increasing the EGR rate. On the other hand, in the same injection timing conditions, CO, HC, <TEX>$CO_2$</TEX> emissions were increased with increasing the EGR rate.

Effect of injection-strategy on combustion, performance and emission characteristics in a DI-diesel engine fueled with diesel from direct coal liquefaction

The performance and exhaust emissions of diesel engine fueled with diesel from direct coal liquefaction (DDCL) with multiple-injection strategy were investigated in this study. Experimental study was conducted on a four-cylinder direct-injection engine, with the injection parameters (main injection timing, pilot injection quantity and timing, and post injection quantity and timing) adjusted to investigate their influences on combustion and emissions. It is found that with the retard of main injection timing, the ignition delay of main combustion is prolonged. Nitrogen oxides (NOX) are decreased by 64.1%, meanwhile, soot is less than 0.051/m. And main injection timing is fixed at −1° crank angle (°CA) before top dead center (BTDC), both the pilot and post injections are introduced to further reduce NOX and soot emissions. Pilot injection, especially early pilot injection (such as 44.5°CA BTDC in this study), continues to reduce NOX emissions with an acceptable level of soot emission. Moreover, both retarding-main injection and pilot injection are the effective ways of reducing the combustion noise. Post injection can decrease NOX and soot emissions simultaneously. There is a specific post injection, at which minimum NOX and soot emissions are achieved, but a slight increase of hydrocarbon (HC) and carbon monoxide (CO) emissions are inescapable.

Effects of pilot injection timing and EGR on a modern V6 common rail direct injection diesel engine

Nitric oxide and smoke emissions in diesel engine can be controlled by optimising the air/fuel mixture. Early injection produces premixed charge resulted in simultaneous NOx and smoke emissions reduction. However, there could be an increase in hydrocarbons and CO emissions due to fuel impinged to the cylinder wall. The focus of the present work is to investigate the effects of a variation of pilot injection timing with EGR to NOx and smoke level on a modern V6 common rail direct injection. This study is carried out at two different engine load conditions of 30 Nm and 55 Nm, at constant engine speed of 2000 rpm. The results show that the early pilot injection timing contributed to the lower smoke level and higher NOx emissions. The higher level of NOx is due to higher combustion temperatures resulting from the complete combustion. Meanwhile, the lower smoke level is due to complete fuel combustion and soot oxidation. The early pilot injection timing produces an intermediate main ignition delay which also contributed to complete combustion. The formation of smoke is higher at a high engine load compared with low engine load due to the higher amount of fuel being injected.

An Experimental Study on Smoke Reduction Effect of Post Injection in Combination With Pilot Injection for a Diesel Engine

With the universal utilization of the common-rail injection system in automotive diesel engines, the multistage injection strategies have become typical approaches to satisfy the increasingly stringent emission regulations, and especially the post injection has received considerable attention as an effective way for reducing the smoke emissions. Normally the post injection is applied in combination with the pilot injection to restrain the NOx emissions, smoke emissions, and combustion noise simultaneously, and the pilot injection condition affects the combustion process of the main injection and might affect the smoke reduction effect of the post injection. Thus this study aims at obtaining the post injection strategy to reduce smoke emissions in a diesel engine, where post injection is employed in combination with pilot injection. The experiments were performed using a single-cylinder diesel engine under various conditions of pilot and post injection with a constant load at an IMEP of 1.01 MPa, fixed speed of 1500 rpm, and NOx emissions concentration of 150 ± 5 ppm that was maintained by adjusting the EGR ratio. The injection pressure was set at 90 MPa at first, and then it was varied to 125 MPa to evaluate the effects of post injection on the smoke reduction in the case of higher injection pressure. The experimental results show that small post injection quantity with a short interval from the end of main injection causes less smoke emissions. And larger pilot injection quantity and later pilot injection timing lead to higher smoke emissions. And then, to explore and interpret the smoke emissions tendencies with varying pilot and post injection conditions, the experimental results of three-stage injection conditions were compared to those of two reference cases, which only included the pilot and main injection, and the interaction between main spray flames and post sprays was applied for analysis. Based on the comparative analysis, the larger smoke reduction effect of post injection was observed with the larger pilot injection quantity, while it is not greatly influenced by pilot injection timing. In addition, the smoke emissions can be reduced considerably by increasing the injection pressure, however the smoke reduction effect of post injection was attenuated. And all of these tendencies were able to be interpreted by considering the intensity variation of the interaction between main spray flames and post sprays.

Impact of DME as an Oxygenated Alternative Fuel on Combustion and Emissions Reduction in a Transportation Vehicle at Low Load Condition

AbstractThis study investigates the impact of dimethyl ether (DME) on the combustion and exhaust emission characteristics at low engine load operating and pilot injection conditions in a four-cylinder diesel engine that was modified for DME application. The combustion characteristics were analyzed based on the combustion pressure, the rate of heat release, the accumulated heat release, and the premixed combustion characteristics. The emission characteristics were analyzed through the analysis of the nitrogen oxides (NOx), soot, hydrocarbon (HC), and carbon monoxide (CO). The heat release amount per unit crank angle in DME combustion is higher than that in diesel combustion in a pilot injected combustion mode. The accumulated heat release of DME during the main combustion is higher than that of diesel fuel. The pilot injection combustion of DME fuel started earlier than single-injection combustion does. The advanced pilot injection timing caused a decrease of premixed combustion duration and a retardation ...

Effects of pilot injection timing on the combustion and emissions characteristics in a diesel engine using biodiesel–CNG dual fuel

Combustion and emissions characteristics of a compression ignition engine with a dual fuel (biodiesel–CNG) combustion system were investigated in this study. This experiment utilized a biodiesel pilot injection to ignite a main charge of compressed natural gas (CNG). The pilot injection pressure was maintained at approximately 120MPa while the pilot injection timing was varied across the range 11–23 crank angle degrees (CAD) before top-dead-center (BTDC) to investigate the characteristics of engine performance and exhaust emissions in a single cylinder diesel engine. Results show that performance can be optimized for biodiesel–CNG dual fuel combustion (DFC) by advancing the pilot injection timing for low loads and delaying the injection timing for high loads. However, overall performance of diesel single fuel combustion (SFC) still exceeds that of biodiesel–CNG DFC. Slight cycle-to-cycle variations are observed when dual fuel is used, but remains less than 1.3% at all conditions. The combustion of biodiesel–CNG begins at a later CAD compared to that of diesel SFC due to the increase of ignition delay of the pilot fuel. The ignition delay in DFC is 1.6–4.4 CAD longer than that of the diesel SFC. Ignition delays are reduced with the increased engine load. BSEC of biodiesel–CNG DFC improves with advanced pilot injection timing at low load and with delayed pilot injection timing at full load. Smoke is decreased and NOx is increased with advanced pilot injection timing in the biodiesel–CNG DFC. Compared to the diesel SFC, however, smoke emissions are significantly reduced over the range of operating conditions and NOx emissions are also reduced except for the full load condition. DFC yields lower CO2 emissions compared to diesel SFC over all engine conditions. Biodiesel–CNG DFC results in relative high CO and HC emissions at low load conditions due to the low combustion temperature of CNG but no notable trend of HC emissions with variations of pilot injection timing were discovered.

Effects of pilot fuel quantity on the emissions characteristics of a CNG/diesel dual fuel engine with optimized pilot injection timing

For CNG/diesel dual fuel engines, the effects of pilot fuel quantity and injection timing are noticeable and significant. In this study, the emission characteristics of a CNG–diesel dual fuel engine with different pilot diesel fuel quantity and optimized pilot injection timing were investigated. The CO emission levels under dual fuel mode are considerably higher than that under normal diesel operation modes even at high load, which indicated that there exist some flame extinction regions. Dual fuel mode reduces NOx emissions by 30% averagely in comparison to diesel mode. That is because most of the fuel is burned under lean premixed conditions which result in lower local temperature. The unburned HC emissions under dual-fuel mode are obviously higher than that of the normal diesel mode, especially at low to medium loads. And around 90% of the THC emissions were unburned methane, which means the flame does not propagate throughout the charge. THC emissions reduce significantly with the increase of the pilot diesel quantity. Thanks to the premixed nature of the combustion mode and the methane molecular structure, the PM emission is reduced obviously under dual fueling condition. The PM emission is increased with the increase of the pilot fuel quantity.