Natural Gas-diesel Dual-fuel Engine Research Articles

An Experimental Study on the Effect of Intake Pressure on a Natural Gas-Diesel Dual-Fuel Engine

Abstract Natural gas-diesel dual-fuel (NDDF) combustion can be a viable method to reduce diesel usage in compression ignition (CI) internal combustion engines. Potential benefits of NDDF engines in comparison to conventional diesel engines include decreases in soot and carbon dioxide emissions. This study focuses on the effect of intake pressure on a dual-fuel engine with intake port injected natural gas (NG) and direct injected diesel at two engine operation conditions – low load-high speed and high load-low speed. The research work was performed on a heavy-duty, single-cylinder engine at a NG-diesel energy ratio of approximately 3:1. The results show that when the intake pressure was increased, the indicated thermal efficiency (ITE) increased for diesel combustion. The trend was similar at the high load-low speed condition but opposite at the low load-high speed condition for NDDF. ITEs of diesel combustion were generally higher than NDDF combustion due to higher unburned hydrocarbon (HC) emissions associated with the latter. For low load-high speed dual-fuel combustion, increasing intake pressure increased the HC and soot emissions, but decreased the nitrogen oxides (NOx) emissions. For high load-low speed case, increasing intake pressure caused the HC emissions to increase and the NOx and soot emissions to decrease. In-cylinder temperature measured at the tip of the diesel injector showed that the injector tip temperatures were higher for NDDF cases compared to diesel cases. These temperatures could be correlated with the combustion phasing and NOx emissions.

Numerical investigation of soot formation in methane/n-heptane laminar diffusion flame doped with hydrogen at elevated pressure

The addition of hydrogen in a dual-fuel mode based on natural gas and diesel offers great potential for improving engine efficiency and reducing emissions. Therefore, detailed numerical simulations have been used to explore the effects of soot formation characteristics of natural gas-diesel dual-fuel engines doped by hydrogen at elevated pressure. Numerical simulations are compared with available experimental data, the effects of H2 addition on soot formation in laminar CH4 + n-heptane, H2 + CH4 + n-heptane, FH2 + CH4 + n-heptane diffusion flames at 2, 4, 6 and 8 atm are simulated, FH2 is added to separate the H2 chemical effects. The results show that the dilution and thermal effects of H2 inhibit soot formation, while the chemical effects of H2 promote soot formation under different pressures. The addition of H2 increases the concentration of H and OH radicals, which promotes the formation of C2H2 and benzene (A1). By simplifying the reaction path and analyzing the production rate of A1, the mechanism of H2 addition to promote A1 formation is illustrated. The concentrations of polycyclic aromatic hydrocarbon (PAH) pyrene (A4), benzo(ghi)fluoranthene (BGHIF) and benzo(a)pyrene (BAPYR) are inhibited at higher pressures that result in lower inception and condensation rates. Therefore, the increase of hydrogen abstraction acetylene addition (HACA) rate is the main reason for the increase of soot formation under chemical effects. While the O2 oxidation rate decreases and the OH oxidation rate increases, that is due to the decrease of O2 concentration and the increase of OH concentration in the soot formation area under chemical effects.

Effects of natural gas admission location and timing on performance and emissions characteristics of LPDF two-stroke engine at low load

Low-pressure gas-admission marine two-stroke engines have significant potential for reducing emissions in the shipping industry. However, they exhibit poor combustion quality under low-load conditions, leading to lower thermal efficiency and high levels of HC and CO emissions. This study numerically evaluated the impacts of the gas admission location and timing on engine performance and exhaust gas emissions under low load conditions. The study revealed that different gas admission locations form distinct NG-air stratifications. Lower gas admission locations resulted in longer ignition delays and shorter combustion durations. The unburned CH4 and CO emissions were significantly reduced by a maximum of 20.14% and 42.29%, respectively. A trade-off exists between NOx and N2O emissions owing to the different temperature conditions of their formation. The NOx emissions increased continuously as the gas admission location was lowered to a maximum of 3.4218 g/kWh; a value slightly above the Tier III emission standards. Advancing the timing of gas admission further decreased the ignition delay time, NOx, and unburned CH4 emissions. This study revealed that in-cylinder natural gas mixture stratification due to varying gas admission locations and timings can improve the combustion efficiency and exhaust gas emissions of a natural gas-diesel dual-fuel engine under low-load conditions.

Optimizing combustion and emissions in natural gas/diesel dual-fuel engine with pilot injection strategy

For the clean and efficient operation of agricultural power, a non-road common-rail engine was modified to achieve natural gas/diesel dual-fuel (NDDF) combustion mode. Under low load conditions, NDDF combustion deteriorates and fuel economy decreases due to lower pressure and temperature inside the cylinder. Therefore, effects of injection pressure, pilot injection timing (SOIpilot) and pilot injection quantity (Qpilot) on in-cylinder combustion, emission characteristics and fuel economy of NDDF engine with pilot injection strategy were investigated at low load. Results show that with the increment of injection pressure, the diesel fuel beam penetration distance increased, prompting the diesel more quickly and fully mixed with fresh charge. The maximum in-cylinder pressure increased, the combustion center (CA50) moved forward, the ignition delay period was shortened, and soot, HC, C2H4 and C3H6 emissions were reduced, while BTE was improved. When SOIpilot moved forward, the pilot injected diesel and natural gas were more fully mixed, which promoted the generation of activation radicals and combustion intensity of main injected diesel. Pmax first increased and then decreased, the peak value of first heat release rate (HRRP1) gradually decreased, the peak value of second heat release rate (HRRP2) continuously increased, the combustion duration decreased, and the soot, CO and HC emissions decreased. At SOIpilot = −30 °CA ATDC, unregulated emissions reached the lowest level, while BTE was 35.55 %. With the increment of Qpilot, both Pmax and HRRP1 increased, CA05 and CA50 moved forward, combustion duration was extended, COV decreased significantly, and all emissions except NOx decreased, especially aldehyde emissions.

Effects of Adding Ethanol to Natural Gas-Air Mixture on Combustion and Emissions of Natural Gas-Diesel Dual Fuel Engine Based on GT-Power

ABSTRACT To resolve power reduction and engine knock, we investigate the influence of adding ethanol to the natural gas (NG)-air mixture on the combustion and emissions of NG-diesel dual-fuel (NDDF) engines by numerical analysis. The baseline engine is a 4-cylinder diesel engine. NG and ethanol fuels are injected into the intake port, while diesel fuel is injected directly into the cylinder. The simulation is performed using GT-Power software, and the results are validated using experimental data. The engine speeds are set at 1000, 1800, and 2800 rpm. The engine loads are set at 50% and 75%. The diesel injection ratios are 10% and 20%. The ethanol substitution rate (ESR) varies from 0% to 60% with an interval of 10%. The results indicate that combustion and emissions are improved with the increase in ESR. First, the engine knock is reduced since the maximum pressure rise rate (MPRR) decreases. Second, the power performance and economy performance of the NDDF engine is improved because the indicated thermal efficiency (ITE) and brake mean effective pressure (BMEP) increase. In addition, although the emissions of the NG-ethanol-diesel ternary-fuel engine are higher than that of NDDF engines, some emissions, such as nitrogen oxide (NOx) emissions and carbon monoxide (CO) emissions, are lower than that of pure diesel engines. This suggests that the addition of ethanol can improve the power and economic performance of NDDF engines.

Comparative evaluation of conventional dual fuel, early pilot, and reactivity-controlled compression ignition modes in a natural gas-diesel dual-fuel engine

Comparative evaluation of conventional dual fuel, early pilot, and reactivity-controlled compression ignition modes in a natural gas-diesel dual-fuel engine

Experimental study on in-cylinder combustion and exhaust emissions characteristics of natural gas/diesel dual-fuel engine with single injection and split injection strategies

On a non-road, high-pressure common-rail engine, natural gas/diesel dual-fuel (NDDF) combustion mode was performed. The way natural gas energy substitution percentage (ESP) and pilot diesel injection timing affected the combustion process, emission properties and fuel economy regarding NDDF engine with single injection strategy and split injection strategy was experimentally investigated at 25% load of 1800 rpm. Results show that under the two injection strategies, as ESP increased, NDDF combustion altered from single-stage to two-stage slowly, the combustion center (CA50) was delayed, the combustion duration increased, the soot and NO emissions declined, and the brake thermal efficiency (BTE) presented an increase-to-decrease change trend. As the combustion phase of split injection strategy was wholly advanced, the ignition delay period was shortened, the cyclic coefficient of variation (COV) and HC emission declined, and the BTE elevated. Additionally, the advanced injection timing would make NDDF heat release gradually advance, resulting in advanced CA50, extended ignition delay, lengthened combustion duration, lowered unregulated emissions, and increased BTE. The increase in peak heat release rate and BTE of split injection strategy was accompanied by decreased HC and aldehyde emissions. For NDDF engine possessing optimized split injection strategy, the BTE reached 37.79% and the COV reached 1.49% at ESP= 60%.

Numerical research of the in-cylinder natural gas stratification in a natural gas-diesel dual-fuel marine engine

The urgent need for decarbonization and emission reduction for marine engines is driving the development of alternative low-carbon fuels. One of the best alternative fuels for engines is natural gas, a clean energy source with vast reserves and a low price. However, low-pressure injection dual-fuel engines exhibit poor combustion characteristics at low engine loads, and extinction is likely to occur in the fuel mixture's dilution region. Thus, the Low Pressure Post Injection (LPPI) strategy was proposed in this paper. The major objective of the LPPI mode is to increase monocirculation combustion stability under low to moderate engine loads by achieving a reasonable distribution of NG in the combustion chamber. LPPI was compared with the Low Pressure Injection (LPI) strategy. Results indicate that the LPPI mode could successfully raise the swirl ratio in the cylinder upto 60.7 percent while perfectly avoiding the NG leakage phenomena. Additionally, with the aid of radial-wall distribution of NG and an improved swirl ratio in LPPI mode, the combustion duration is reduced by 33.6 percent, and the lean burn limit of the dual-fuel marine engine can be expanded to 0.30. Although local higher combustion temperature caused an large increase in NOx emission which is more than three times than LPI NOx emission, LPPI mode still meets Tier III NOx emission requirements.

Synergistic effect of swirl flow and prechamber jet on the combustion of a natural gas-diesel dual-fuel marine engine

The increasing demands on decarbonization and emission reduction for marine engines are urgently driving the development of efficient and clean combustion technologies for low-carbon fuels. In this work, the combustion of a natural gas (NG)-diesel dual-fuel marine engine was numerically investigated, with particular interest on the synergistic effect of swirl flow and prechamber jet on the mixture formation and flame propagation. Results show that the scavenging port angle governs in-cylinder NG stratification. Specifically, at a small scavenging port angle, NG mainly distributes on the piston top and exhibits a “top lean, bottom rich” stratification pattern; at a large scavenging port angle, NG mainly distributes on the lateral of the cylinder and forms a “inner lean, outer rich” stratification pattern, which is preferred since prechamber ignition favors rich mixture, provided that the swirl ratio is not excessively large to yield reduced scavenging efficiency. Moreover, the prechamber layout significantly affects the swirl motion and the high-speed jet flame propagation. Utilizing multiple prechambers shortens the flame propagation distance and suppresses the sensitivity of ignition on the non-uniform mixture distribution. With the increase of the prechamber channel angle, flame propagation is speeded up due to enhanced swirl flow, while the wall heat loss is also increased, yielding a maximum combustion rate at an intermediate prechamber channel angle of approximately 20°. By synergistically coordinating the scavenging swirl and the prechamber ignition jet, the indicated specific gas consumption was optimized within the Tier III NOx emission limit. The present results are helpful for the development of the combustion system for dual-fuel marine engines.

Parameter investigation of the pilot fuel post-injection strategy on performance and emissions characteristics of a large marine two-stroke natural gas-diesel dual-fuel engine

This study aimed to conduct a parametric study to investigate the effect arising from pilot fuel post-injection strategy on engine combustion, performance, and emissions of a large two-stroke natural gas-diesel dual-fuel engine for marine applications. The one-dimensional and three-dimensional simulation models were built in AVL-BOOST and CONVERGE, respectively, and validated according to experimental results. The effects of post-injection strategies on post-injection timing and mass ratio on engine combustion, performance, and emissions were investigated. As revealed by the results, an appropriate pilot fuel post-injection strategy could achieve lower NOx emissions with less loss of performance. As post-injection timing was delayed, the NOx emission first decreased and then increased. Subsequently, it decreased to the lowest and finally increased. With the increase in the post-injection mass ratio, the NOx emission was kept decreasing. Compared with the original engine, the NOx emission decreased by 81.85 ppm with a post-injection timing of 18 deg after top dead center and with a mass ratio of 0.7. However, the indicated power only decreased by 4.82 kW, and the indicated specific fuel consumption only increased by 0.2 g/kWh. This study can provide some theoretical guidance for the injection strategy optimization of the marine two-stroke natural gas-diesel dual-fuel engines and provide technical suggestions for practical application.

Investigation of Performance and Exhaust Emissions of Compressed Natural Gas-Diesel Dual-Fuel Engine under Different Engine Speed and Load Conditions

Investigation of Performance and Exhaust Emissions of Compressed Natural Gas-Diesel Dual-Fuel Engine under Different Engine Speed and Load Conditions

Effect of pre-main-post diesel injection strategy on greenhouse gas and nitrogen oxide emissions of natural gas/diesel dual-fuel engine at high load conditions

Natural gas/diesel dual-fuel (NDDF) engine technology is an interesting concept for decreasing greenhouse gas (GHG) emissions of heavy-duty diesel engines. One of the main limitations of this concept is the emissions of unburned methane which is estimated to have a GHG potential factor of 25 – 34 over a 100-year period. Our previous study has shown that a NDDF engine using pre-main-post diesel injection strategy can reduce unburned methane emissions, but yields lower indicated thermal efficiency (ITE) and higher carbon dioxide (CO2) and nitrogen oxides (NOx) emissions compared to that using single diesel injection strategy under high engine load conditions due to the advanced combustion phasing. In this study, the combustion phasing of pre-main-post diesel injection strategy is further optimized with the goal to improve the ITE and reduce the GHG and NOx emissions without compromising the unburned methane emissions when compared to single injection strategy. The results reveal that changing pre diesel injection timing gives more controllability of the combustion phasing than changing the main and post diesel injection timing. A more homogenous premixed mixture of pre injected diesel – natural gas – air retards the combustion phasing which allowed further improvement of the ITE and GHG emissions of NDDF engines while maintaining the low unburned methane emissions feature of the pre-main-post injection strategy. It is found that the optimized pre-main-post diesel injection strategy is able to reduce unburned methane, GHG, and NOx emissions by 13.4%, 1.5%, and 42%, respectively, and increase ITE by 0.37% compared to single injection strategy.

Numerical investigation on the combustion and emission characteristics of a heavy-duty natural gas-diesel dual-fuel engine

Natural gas (NG)-diesel dual-fuel combustion is an effective approach to reduce soot and greenhouse gas emissions and mitigate the liquid fossil fuel crisis. In this work, a comprehensive numerical study on the combustion and emission characteristics of a NG-diesel dual-fuel engine operating at the high load condition was performed. Six significant parameters such as the start of injection (SOI) timing, exhaust gas recirculation (EGR), injection and intake pressures, nozzle number, and NG substitution ratio were investigated. A pathway to achieve highly efficient and clean combustion was proposed. It was demonstrated that at least an EGR rate of 40% should be employed to meet the NOx Euro VI regulation limit. Although a higher injection pressure enhanced the diesel-air mixing process and promoted engine efficiency, the highest achievable engine efficiencies were similar using different injection pressures. An elevated intake pressure with an earlier SOI timing promoted the oxidation process. Therefore, it resulted in a lower combustion loss and thus higher engine efficiency. Furthermore, the increase of nozzle number effectively promoted the air utilization rate and expedited the combustion heat release, which resulted in a higher engine efficiency but lower soot emission. But the growing trend of engine efficiency was limited and a nozzle number of 11 was found to be the optimal option. Finally, a peak engine efficiency of about 47.6% was achieved with a NG substitution ratio of 95% and an optimized SOI timing, and meanwhile, both the NOx and soot emissions were below the Euro VI emission regulation limits.

Effect of post-injection strategy on greenhouse gas emissions of natural gas/diesel dual-fuel engine at high load conditions

In this study the effect of two diesel injection strategies named main-post and pre-main-post on natural gas/diesel dual-fuel (NDDF) combustion at high load conditions is investigated. In the main-post diesel injection strategy, part of diesel is injected after the main injection in the late expansion stroke (post-injection). In the pre-main-post injection strategy, part of diesel fuel is injected before main injection in the early compression stroke (pre-injection) and part of diesel fuel is injected after main injection in the late expansion stroke. The results revealed that the main-post diesel injection strategy did not change the start of combustion compared to single injection strategy. However, the pre-main-post injection strategy significantly increased the cylinder pressure and advanced the start of combustion. The maximum measured indicated fuel efficiencies (IFE) of NDDF engine with both single and pre-main diesel injection strategies were 41.50%. The main-post diesel injection strategy slightly decreased IFE of NDDF (i.e., 40.35%). However, an optimized combustion phasing and pre-main-post injection strategy made it possible to achieve similar or higher IFE than single injection strategy. Moreover, the pre-main-post diesel injection strategy significantly decreased unburned methane emissions. The lowest measured unburned methane emissions when using pre-main-post diesel injection was 0.37 g/kW.h, which was lower than that of single injection (0.80 g/kW.h). Compared to single diesel injection, optimized combustion phasing along with pre-main-post injection strategy reduced GHG and NOx emissions by 10% and 47%, respectively.

Numerical investigation of natural gas-diesel dual-fuel engine with different piston geometries and radial clearances

Piston crevices are the major source of hydrocarbon emissions for spark ignition engine. It is similar for natural gas-diesel (NG-diesel) dual fuel engine, maybe even worse in high compression ratio and lean burn NG-diesel engine at low load. The aim of this paper is to numerically investigate combustion and methane emissions of YC-6K NG-diesel engine with different radial clearances. Four piston clearances (0.5 mm, 0.76 mm, 1.0 mm and 1.54 mm) and four different piston geometries were employed. Three diesel-spray-orientated (DSO) piston bowls were designed based on diesel injectors of YC-6K with the purpose of supplying more natural gas and air mixture to diesel spray jets, in addition, a protrusion-ring was designed at the bowl rim of DSO pistons to enhance methane flame propagation. The results showed that both in-cylinder pressure and heat release rate (HHR) of all three DSO pistons increased due to higher turbulence kinetic energy comparing to the original piston design (OPD). Methane emissions of pistons with radial clearance of 0.76 mm were lower than that of other radial clearances for DSO pistons.

A Study on the High Load Operation of a Natural Gas-Diesel Dual-Fuel Engine

Diesel fueled compression ignition engines are widely used in power generation and freight transport owing to their high fuel conversion efficiency and ability to operate reliably for long periods of time at high loads. However, such engines generate significant amounts of carbon dioxide (CO2), nitrogen oxides (NOx), and particulate matter (PM) emissions. One solution to reduce the CO2and particulate matter emissions of diesel engines while maintaining their efficiency and reliability is natural gas (NG)-diesel dual-fuel combustion. In addition to methane emissions, the temperatures of the diesel injector tip and exhaust gas can also be concerns for dual-fuel engines at medium and high load operating conditions. In this study, a single cylinder NG-diesel dual-fuel research engine is operated at two high load conditions (75% and 100% load). NG fraction and diesel direct injection (DI) timing are two of the simplest control parameters for optimization of diesel engines converted to dual-fuel engines. In addition to studying the combined impact of these parameters on combustion and emissions performance, another unique aspect of this research is the measurement of the diesel injector tip temperature which can predict potential coking issues in dual-fuel engines. Results show that increasing NG fraction and advancing diesel direct injection timing can increase the injector tip temperature. With increasing NG fraction, while the methane emissions increase, the equivalent CO2emissions (cumulative greenhouse gas effect of CO2and CH4) of the engine decrease. Increasing NG fraction also improves the brake thermal efficiency of the engine though NOx emissions increase. By optimizing the combustion phasing through control of the DI timing, brake thermal efficiencies of the order of ∼42% can be achieved. At high loads, advanced diesel DI timings typically correspond to the higher maximum cylinder pressure, maximum pressure rise rate, brake thermal efficiency and NOx emissions, and lower soot, CO, and CO2-equivalent emissions.

Numerical analysis of economic and environmental benefits of marine fuel conversion from diesel oil to natural gas for container ships.

Shipping is a significant contributor to global greenhouse gas (GHG) and air pollutant emissions. These emissions mainly come from using diesel fuel for power generation. In this paper, the natural gas is proposed as an alternative marine fuel to be used instead of conventional marine diesel oil. Numerical analysis of environmental and economic benefits of the natural gas-diesel dual-fuel engine is carried out. As a case study, a container ship of class A7 owned by Hapag-Lloyd has been investigated. The results show that the proposed dual-fuel engine achieves environmental benefits for reducing carbon dioxide (CO2), nitrogen oxides (NOx), sulfur oxides (SOx), particulate matter (PM), and carbon monoxide (CO) emissions by 20.1%, 85.5%, 98%, 99%, and 55.7% with cost effectiveness of 109, 840, 9864, 27761, and 4307US$/ton, respectively. The results show that the conversion process to the dual-fuel engine will comply with the current and future IMO regulations regarding air pollutant emissions. On the other hand, using the proposed dual-fuel engine on the container ship will improve the ship energy efficiency index by 29.6 % with annual fuel cost saving of 4.77 million US dollars.

On the Variation of the Effect of Natural Gas Fraction on Dual-Fuel Combustion of Diesel Engine Under Low-to-High Load Conditions

Natural gas-diesel dual fuel (NDDF) engine has the potential to significantly reduce carbon dioxide (CO2) and particulate matter (PM) emissions, while retaining diesel engine’s high efficiency and reliability. The operation and performance of NDDF engine depend on natural gas energy fraction (%NG), which ranges from low %NG, where diesel fuel provides most of the combustion energy, to high %NG where diesel fuel is used only to initiate combustion. Although pertaining published studies demonstrated that the effect of %NG on the combustion performance and emissions of NDDF engine depend upon the engine load, none of these studies discussed the reasons behind this dependence. The present study attempts to shed light on this issue by experimentally and numerically investigating the effect of different %NGs on NDDF engine under different load conditions. Both experimental and numerical results revealed that the peak pressure rise rate (PPRR) first increases and then drops with increasing %NG under all load conditions. The calculated local equivalence ratio and charge temperature contours showed that increasing %NG to a certain limit increases local equivalence ratio inside the ignition kernel which implies that more premixed natural gas – air mixture participates in reactions during the premixed combustion stage. This results in an increased flame temperature and higher PPRR right after ignition. However, increasing %NG beyond this range decreases local equivalence ratio inside the ignition kernel which leads to lower PPRR. Increasing %NG retards the combustion phasing at low to medium load conditions. However, increasing %NG generally advances the combustion phasing under medium to high load conditions due to the fact that the flame propagation speed of natural gas – air mixture increases with %NG at medium to high load conditions. Methane emissions grow with increasing %NG under all examined engine load conditions. However, this growth becomes much smaller under medium to high engine load conditions. Increasing %NG significantly increases GHG emissions under lower load conditions. However, using advanced diesel injection timing decreases GHG emissions of NDDF engine under lower load conditions. Increasing %NG decreases GHG emissions by 6 to 11% under medium to high load conditions.

Split diesel injection effect on knocking of natural gas/diesel dual-fuel engine at high load conditions

Advancing the start of diesel injection timing is an effective way to enhance thermal efficiency and reduce greenhouse gas (GHG) emissions of natural gas/diesel dual-fuel (NDDF) engine. However, severe thermodynamic conditions under high engine load conditions may increase the propensity for engine knocking when advancing the start of diesel injection (SODI). In this study, the strategy of split diesel injection (two-pulse injection) is used and its feasibility as a method to reduce knocking intensity and improve thermal efficiency of NDDF engine is investigated. The results reveal that advancing single diesel injection timing significantly increases knocking intensity, whereas split diesel injection strategy decreases knocking intensity. The results also show that, when using split diesel injection, the flame kernels do not propagate as fast and deep as in the case of single diesel injection. This slows down the pressure and temperature rise rate in the unburned end-gas region and thus reduces knocking tendency. Moreover, the early partially burning of the premixed natural gas – air mixture in the squish region dilutes the unburned end-gas and consequently makes it resistant to auto-ignition. NDDF engine with split diesel injection can reach a maximum thermal efficiency that is comparable to that observed under knocking conditions of single diesel injection. Using either, single or split, diesel injection strategy reduces GHG emissions of NDDF engine (up to 12%) compared to its counterpart diesel engine. However, the lowest GHG emissions of NDDF engine with single diesel injection strategy is recorded under knocking conditions.

Experimental Study on Combustion and Performance of a Natural Gas-Diesel Dual-Fuel Engine at Different Pilot Diesel Injection Timing

Abstract The pilot diesel injection timing (θ) significantly affects the combustion and performance of dual-fuel (DF) engines. In order to optimize the θ of a natural gas-diesel DF engine, the influence of θ on combustion, cyclic variation, and performance of a diesel engine fueled with natural gas piloted by diesel under full load at 1200 rpm was investigated. The results indicate that, with the advance in θ, the cylinder pressure, rate of pressure rise (ROPR), and heat release rate (HRR) increase first and then decrease. The mean value of peak cylinder pressure (pmax) rises and the standard deviation increases first and then decreases. The distribution of the crank angle of peak cylinder pressure (φ(pmax)) scatters and approaches the top dead center. The coefficient of variation (COV) in pmax decreases first and then increases while the COV in φ(pmax) obviously increases. The brake power increases first and then decreases while the brake specific fuel consumption (b.s.f.c.) reduces first and then rises. The CO2 and NOx emissions rise first and then reduce while smoke emission decreases first and then increases, but the CO and HC rise.