Natural Gas Direct Injection Research Articles

Optimization of the injection parameters of a diesel/natural gas dual fuel engine with multi-objective evolutionary algorithms

In this study, the injection parameters of a High-Pressure Direct-Injection (HPDI) natural gas engine was optimized by coupling a multi-dimensional computational fluid dynamics (CFD) code with the genetic algorithm (GA). Moreover, the analysis of the combustion and emission characteristics of a diesel/natural gas dual fuel engine are performed in this paper with the introduction of the diesel/natural gas dual fuel injection model into the CFD code. The result reveals that the developed gas fuel injection model is capable to predicate the penetrations of the natural gas injection. For the dual fuel engine with simultaneous reduction of NOx and soot, the optimized diesel injection timing is at −15.2 °CA ATDC, the gas injection timing is around −6.0 °CA ATDC, and the circumferential offset angle between the diesel and natural gas nozzle hole is around 8.8°. The lowest ISFC condition is achieved when the injection interval between the diesel and natural gas is 1.38 °CA. For the high soot emissions cases, the gas injection timings are later compared with the other cases. In the dual fuel engine, most of the NO emissions are generated through the combustion of the direct injected natural gas. Soot formation region is mainly located in the squish volume close to the cylinder walls, where the temperature is low which leads to a lower soot oxidation rate.

Soot emission prediction in pilot ignited direct injection natural gas engine based on n-heptane/toluene/methane/PAH mechanism

A dual fuel mechanism for pilot ignited direct injection natural gas engine was developed. Fuel blend of n-heptane and toluene was selected as the surrogate fuel for diesel, methane was selected as the surrogate fuel for natural gas. A reduced mechanism was adopted for methane oxidation while three skeletal mechanisms were used for n-heptane oxidation, toluene oxidation as well as PAH formation and growth respectively. The sub-mechanisms were then integrated into a complete mechanism with 84 species and 336 steps. Based on the mechanism, a 3D simulation model was built for pilot ignited direct injection natural gas engine and was then used to evaluate the effects of different natural gas post injection strategies and EGR addition. The simulation results indicated that CO and soot emissions can be effectively reduced with the adoption of natural gas post injection strategy, however, sacrifices in NOx emissions will be accompanied. With the addition of EGR, the higher NOx emissions resulted from the adoption of the post injection strategies could be avoided. Therefore, it can be concluded that the combined use of the natural gas post injection strategy and EGR addition is an effective way for the achievement of the engine optimized performance.

Large-eddy simulation of direct injection natural gas combustion in a heavy-duty truck engine using modified conditional moment closure model with low-dimensional manifold method

This article describes the application of a modified first-order conditional moment closure model used in conjunction with the trajectory-generated low-dimensional manifold method in large-eddy simulation of pilot ignited high-pressure direct injection natural gas combustion in a heavy-duty diesel engine. The article starts with a review of the intrinsic low-dimensional manifold method for reducing detailed chemistry and various formulations for the construction of such manifolds. It is followed by a brief review of the conditional moment closure method for modelling the interaction between turbulence and combustion chemistry. The high computational cost associated with the direct implementation of the basic conditional moment closure model was discussed. The article then describes the formulation of a modified approach to solve the conditional moment closure equation, whose reaction source terms for the conditional mass fractions for species were obtained by projecting the turbulent perturbation onto the reaction manifold. The main model assumptions were explained and the resulting limitations were discussed. A numerical experiment was conducted to examine the validity the model assumptions. The model was then implemented in a combustion computational fluid dynamics solver developed on an open-source computational fluid dynamics platform. Non-reactive jet simulations were first conducted and the results were compared to the experimental measurement from a high-pressure visualization chamber to verify that the jet penetration under engine relevant conditions was correctly predicted. The model was then used to simulate natural gas combustion in a heavy-duty diesel engine equipped with a high-pressure direct injection system. The simulation results were compared with the experimental measurement from a research engine to verify the accuracy of the model for both the combustion rate and engine-out emissions.

Performance and emissions of a compression-ignition direct-injected natural gas engine with shielded glow plug ignition assist

Performance and emissions experiments were conducted on a compression-ignition direct-injected natural gas engine (DING) equipped with a shielded glow plug ignition assist system. Tests were conducted at three different intake pressures (34.5 kPag, 68.9 kPag, 103.4 kPag), and four nominal (targeted) equivalence ratios (0.2, 0.3, 0.4, 0.5). CH4, NOx, CO and PM emissions were measured and analyzed, showing that emissions levels are influenced by the DING engine’s combustion modes and intake pressure. Premixed combustion which dominates at low equivalence ratios resulted in higher levels of CH4 and NOx emissions, while mixing-controlled combustion, which develops at higher equivalence ratios, resulted in elevated CO and PM levels. Higher intake pressure was found to improve all emissions levels. The most significant effect was the reduction of PM and CO emissions due to improved fuel charge mixing and air entrainment that results from a pressure-driven momentum increase of the engine’s air swirl field. Brake specific emissions and fuel consumption were estimated and compared against levels reported in the literature for dual-fuel port-injection, and High-Pressure Direct-Injection (HPDI) natural gas engines. The most significant finding was that the DING engine exhibits lower fuel consumption and PM emissions levels when compared to values reported in the literature for HPDI engines. The PM emissions advantage was attributed to a higher proportion of premixed combustion and the absence of a diesel pilot in DING engine operation. Lastly, PM size distributions were analyzed, showing that the DING engine produces PM that is smaller than PM of a conventional diesel engine, but similar to the PM reported in the literature for HPDI engines.

Potential of direct-injection for the improvement of homogeneous-charge combustion in spark-ignition natural gas engines

The direct-injection has been considered as a way to improve the performance of conventional spark-ignition natural gas engines with the port-fuel-injection by increasing the engine volumetric efficiency. However, insufficient attention has been paid to the potential of direct-injection for the combustion and thermal efficiency improvement of homogeneous-charge combustion in natural gas engines that can be achieved by the spray-induced turbulence enhancement of the in-cylinder fuel–air mixture. The current study investigates the engine thermal efficiency, combustion speed, combustion stability and hydrocarbon emissions of a direct-injection natural gas engine under varied injection timings, and compares the combustion characteristics of the direct-injection with those of port-fuel-injection. Then, a particular engine operation scheme (port-fuel-injection of natural gas and direct-injection of nitrogen) is applied to evaluate the potential of spray-induced turbulence on the thermal efficiency improvement in the homogeneous-charge combustion mode. The results showed that the direct-injection could improve the engine combustion speed, combustion stability and thermal efficiency in low-load conditions as a result of enhanced in-cylinder turbulence at retarded injection timings. Meanwhile, the direct-injection decreased the engine thermal efficiency in high-load conditions and increased the hydrocarbon emissions regardless of the engine load condition due to the deteriorated mixture homogeneity. When the in-cylinder turbulence and mixture homogeneity were both achieved, a few percent of thermal efficiency improvement was obtained by the direct-injection, and the improvement rate increased as the engine load decreased.

Study of Assisted Compression Ignition in a Direct Injected Natural Gas Engine

Natural gas direct injection (DI) and glow plug ignition assist technologies were implemented in a single-cylinder, compression-ignition optical research engine. Initial experiments studied the effects of injector and glow plug shield geometry on ignition quality. Injector and shield geometric effects were found to be significant, with only two of 20 tested geometric combinations resulting in reproducible ignition. Of the two successful combinations, the combination with 0 deg injector angle and 60 deg shield angle was found to result in shorter ignition delay and was selected for further testing. Further experiments explored the effects of the overall equivalence ratio (controlled by injection duration) and intake pressure on ignition delay and combustion performance. Ignition delay was measured to be in the range of 1.6–2.0 ms. Equivalence ratio was found to have little to no effect on the ignition delay. Higher intake pressure was shown to increase ignition delay due to the effect of swirl momentum on fuel jet development, air entrainment, and jet deflection away from optimal contact with the glow plug ignition source. Analysis of combustion was carried out by examination of the rate of heat release (ROHR) profiles. ROHR profiles were consistent with two distinct modes of combustion: premixed mode at all test conditions, and a mixing-controlled mode that only appeared at higher equivalence ratios following premixed combustion.

A holistic investigation of natural gas\u2013diesel dual fuel combustion with dual direct injection for passenger car applications

This publication covers the investigation of a dual fuel combustion process for passenger car applications using natural gas and diesel as fuels. In the literature a widely studied dual fuel concept is the combination of port fuel injection of natural gas and direct injection of diesel. The challenge of this concept is a high emission of unburned hydrocarbons at low load operation as previous publications show. The proposed concept features a low pressure direct injection of natural gas in combination with direct injection of diesel to circumvent this problem. The acronym DDI—dual direct injection is introduced for this concept. It enables charge stratification of the air–natural gas mixture. This allows for a significant reduction of the unburned hydrocarbon emissions as earlier studies already demonstrated. The focus of this publication is on hardware variations which were performed on the engine test bench. Results are presented of a variation of the compression ratio and of different charge motion patterns which were studied. The results are compared with a conventional diesel and a gasoline spark ignited engine. The investigations demonstrate that a CO2 reduction of 20–29% is feasible as compared to conventional engines. Finally, investigations of exhaust gas aftertreatment with a three-way catalyst are published. The aftertreatment of the remaining engine-out hydrocarbon emissions is still the key challenge due to the low exhaust gas temperature during low load operation.

Comparisons of the volumetric efficiency and combustion characteristics between CNG-DI and CNG-PFI engines

In the present study, the volumetric efficiency and combustion characteristics of compressed natural gas (CNG) direct injection (DI) and port fuel injection (PFI) were compared. In a single-cylinder engine, various fuel injection timings were tested for each fuel injection position, and the volumetric efficiency of each test condition was calculated from the intake flow rate. The one-dimensional simulation program AMESim was also used to further investigate the intake process. Experimental and numerical results showed that the volumetric efficiency was not influenced by the position of the injector. For the early fuel injection, before the intake valve close (IVC), the volumetric efficiencies of the DI and PFI were similar to each other; the averaged volumetric efficiencies were both about 38.62% and the standard deviations of volumetric efficiency were less than 0.2%. However, as the fuel injection timing was retarded after the IVC, the volumetric efficiency of DI increased while the volumetric efficiency of PFI was kept constant or slightly decreased. The increase in the volumetric efficiency was due to the fact that the fuel volume did not occupy the cylinder volume during the intake stroke. Combustion was stable for all the test conditions. The coefficient of variation of the indicated mean effective pressure (COVIMEP) was lower than 1.5%. The highest fuel conversion efficiency was observed for late fuel direct injection, after the IVC, due to the fastest combustion. Thus, by applying the late fuel injection timing after IVC, the CNG-DI could have a higher volumetric efficiency and fuel conversion efficiency than the CNG-PFI.

Numerical Studies of Glow Plug Shield on Natural Gas Ignition Characteristics in a Compression-Ignition Engine

This paper presents a numerical study on fuel injection, ignition, and combustion in a direct-injection natural gas (DING) engine with ignition assisted by a shielded glow plug (GP). The shield geometry is investigated by employing different sizes of elliptical shield opening and changing the position of the shield opening. The results simulated by KIVA-3V indicated that fuel ignition and combustion is very sensitive to the relative angle between the fuel injection and the shield opening, and the use of an elliptical opening for the glow plug shield can reduce ignition delay by 0.1–0.2 ms for several specific combinations of the injection angle and shield opening size, compared to a circular shield opening. In addition, the numerical results also revealed that the natural gas ignition and flame propagation will be delayed by lowering a circular shield opening from the fuel jet center plane, due to the blocking effect of the shield to the fuel mixture, and hence, it will reduce the DING engine performance by causing a longer ignition delay.

Combined effect of injection timing and injection angle on mixture formation and combustion process in a direct injection (DI) natural gas rotary engine

The application of direct injection (DI) technology is considered as a key solution to the problems of combustion efficiency and emissions on the rotary engine. This work aimed to numerically study the combined effect of injection timing (IT) and injection angle (IA) on mixture formation and combustion process in the 3D flow field of a DI natural gas rotary engine. On the basis of the 3D dynamic simulation model which was established in our previous work [29, 30], some critical information was obtained which was difficult to acquire through experiment. Simulation results showed that to satisfy the ideal fuel distribution for high combustion rate, a small IA should be used when the IT was at the early stages of intake stroke, and a big IA should be used when the IT was at the early stages of compression stroke. However, when the IT was at the middle and later stages of intake stroke, the IA which could satisfy the ideal fuel distribution, was difficult to determine with the changed IT in the middle and later stage of intake stroke. For the above reason, the middle and late stage of intake stroke was not recommended as injection timing in engineering application.

Effects of injection rate on combustion and emissions of a pilot ignited direct injection natural gas engine

Effects of Injection rates on combustion process and emissions of engines operating with directly injected natural gas and pilot diesel were numerically investigated. Injection rates of natural gas and diesel were investigated separately utilizing five types of injection rates. An impact factor was defined to present the effects of the initial and terminal injection rates of diesel and natural gas on the combustion and emissions more intuitionally. Based on the simulation results, cylinder pressure and temperature were more sensitive to terminal injection rates of pilot diesel than initial injection rates, and lower terminal injection rates of pilot diesel can achieve lower NO and Soot emission level. However, there is a trade-off between NO and Soot emissions affected by different natural gas injection rates. The impact factors of pilot diesel injection rates on pressure show a double-peak trend. However, the impact factors of natural gas injection rates on pressure show a single-peak trend.

Effects of Hydrogen Addition on the Performance of a Pilot-Ignition Direct-Injection Natural Gas Engine: A Numerical Study

Adding hydrogen to natural gas is a promising way to improve the ignition stability and reduce the greenhouse gas emissions of pilot-ignition direct-injection natural gas engines. Most of the previous studies concerning hydrogen-enriched natural gas engines are focused on spark-ignition engines. The limited investigations on the addition of hydrogen in direct-injection natural gas engines are conducted by experimental method. Therefore, some detailed information on the in-cylinder combustion and emission formation process are left unknown. In this work, numerical simulations have been performed for the combustion process of a pilot-ignition direct-injection natural gas engine based on an integrated mechanism which is capable of describing the chemical kinetics involving diesel, natural gas, and hydrogen. Three-dimensional (3D) computational fluid dynamics simulations were conducted at different hydrogen blend ratios to explore the effects of hydrogen addition on the whole combustion process and the mole f...

Numerical analysis of the influence of the fuel injection timing and ignition position in a direct-injection natural gas engine

Large-eddy simulation of fuel injection and combustion in a direct-injection natural gas engine was conducted. The influence of the fuel injection timing and ignition position was numerically analyzed. The engine used in this study operates in lean burn mode with a fuel-air equivalence ratio of approximately 0.72. The combustion pressure and in-cylinder burned volume decrease as fuel is injected earlier using the same ignition timing, and the fuel consumption rate also decreases. As ignition is delayed, the influence of the fuel injection timing is weakened because of the over-mixed mixture during the late compression stoke. Fuel injection timing changes the global fuel-air equivalence ratio, which is not the primary cause of its effect on combustion. As fuel is injected later, the in-cylinder velocity magnitude increases and a relatively richer mixture is distributed around the ignition position, which contributes to better combustion. This is the main mechanism of how fuel injection timing influences combustion. The ignition position determines the background distribution of the velocity magnitude and mixture and confines the available space for flame development. Central ignition is the best choice for the engine used in this study.

Influence of chamber pressure on CNG jet characteristics of a multi-hole high pressure injector

Natural Gas Direct Injection (NGDI) engines have attracted attention of engine manufacturers because of low pollutant emissions and high efficiency. The jet structure and injector properties are control parameters for optimal mixture formation and stable combustion. Here, the jet characteristics are investigated experimentally. The natural gas jet, injected through a multi-hole injector, is visualized using Schlieren photography. The effects of injection and chamber pressures on macroscopic jet characteristics are examined. New correlations for tip speed and tip penetration are presented. Results show that reducing chamber pressure is more effective than injection pressure for increasing the jet axial penetration. Moreover, the linear relation between non-dimensional tip penetration and time is dependent on the chamber-to-injected gas density ratio.

Optimization of the compressed natural gas direct injection in a small research spark ignition engine

The permanent aim of the automotive industry is the further improvement of the engine efficiency and the simultaneous pollutant emissions reduction. In order to optimize the small internal combustion engines, it is necessary to further improve the basic knowledge of the thermo-fluid dynamic phenomena occurring during the combustion process. In this context, the application of optical diagnostic techniques permits a deep insight into the fundamental processes such as flow development, fuel injection, and combustion process. The aim of this study was the optimization of the compressed natural gas direct injection by means of the analysis of the injection phase and combustion process. This analysis allowed the improvement of the engine efficiency in lean-burn operation condition too. The investigation was carried out in an optically accessible small direct injection spark ignition single-cylinder engine. Two different injectors were tested. The first one was the injector designed according to the results of ...

Experimental Investigation of Performance and Emissions of a Stratified Charge CNG Direct Injection Engine with Turbocharger

This paper presents the results from 1.6 litre, 4 cylinders stratified charge compressed natural gas (CNG) direct injection engine with boosting device. A turbocharger with compressor trim of 40 was used to increase engine output. The engine was tested at wide open throttle (WOT) and speed ranging from 1000 to 5000 rpm. Engine performance and emissions data were recorded under steady state condition. Results show turbocharged CNG engine produced an average of 26% increment in brake power and 24% additional maximum brake torque as compared with natural aspirated (NA) CNG engine. Turbocharged CNG engine improved brake specific fuel consumption (BSFC) and yielded higher fuel conversion efficiency (FCE). Relatively turbocharged CNG engine showed lower emission of hydrocarbon (HC) and carbon monoxide (CO) throughout tested engine speed. Conversely, the carbon dioxide (CO 2 ) and nitrogen oxide (NO x ) emission produced were slightly higher compared with NA CNG engine.

The influence of injection strategy on mixture formation and combustion process in a direct injection natural gas rotary engine

The application of direct injection (DI) technology is considered as an effective way to improve the performance of the rotary engine. This work seeks to numerically dissect the influence of injection strategy on mixture formation and combustion process in a DI natural gas rotary engine. A 3D dynamic simulation model established in our previous work was used to acquire some critical information which was difficult to obtain through experimental investigations. These were the flow field, the fuel distribution, the temperature field and some intermediate concentration fields in the combustion chamber. Simulation results showed that for mixture formation, the motion mechanism of the fuel varies with the injection position. The mass of fuel located at the back of the combustion chamber for injection nozzles A, B and C, was determined by the intensity of vortex I, the coupling function between the value of the impact angle and the intensity of vortex I, and the value of the impact angle respectively. In addition, with retarded injection timing, the accumulation area of fuel for all injection nozzle positions moved from the back to the front of the combustion chamber at ignition timing. For combustion process, the overall combustion rate for the injection strategy (case A4) whose nozzle was 50mm apart along the engine major axis and whose injection timing was 360°CA (BTDC), was the fastest. Compared with the out-cylinder premixed gas-filling method (case premix method), the improved combustion rate of case A4 had a 29.7% increase in peak pressure, but also a certain increase in NO emissions.

Influence of Injector Location on Part-Load Performance Characteristics of Natural Gas Direct-Injection in a Spark Ignition Engine

Influence of Injector Location on Part-Load Performance Characteristics of Natural Gas Direct-Injection in a Spark Ignition Engine

Effect of fuel injection timings on performance and emissions of stratified combustion CNGDI engine

This study investigates the effect of various injection timings on the performance and emissions of stratified combustion compressed natural-gas direct injection. The engine of 1.6l, spark ignition, four cylinders fuelled with compressed natural gas was tested. The engine test bed using Kronos software and the exhaust emission were recorded using portable exhaust gas analyser Kane-May. All tests were occurred under wide throttle open with various injection timings (EOI 120, EOI 180, EOI 300, EOI 360)BTDC. Results show high power, torque and brake mean effective pressure (BMEP) at 120BTDC. The lowest brake specific fuel consumption (BSFC) is at 120BTDC. Lambda is shown higher than one, which is mean lean mixture air-fuel. Carbon monoxide (CO) emission is low at 360BTDC at low speeds but at high speed, it was low at 120BTDC. Carbon dioxide (CO2) emission was high at 120BTDC on the high engine speeds. The lowest (NO) and (HC) were founded at 120BTDC. However, the combustion pressure and the PV were recorded for all injection timings under various engine speeds.

Performance, Efficiency and Emissions Assessment of Natural Gas Direct Injection compared to Gasoline and Natural Gas Port-Fuel Injection in an Automotive Engine

Performance, Efficiency and Emissions Assessment of Natural Gas Direct Injection compared to Gasoline and Natural Gas Port-Fuel Injection in an Automotive Engine