Direct Injection Engine Research Articles

Evaluation of Operability and Exhaust Emissions of Common Rail Direct Injection Engine using Biodiesel Blends in Moderate Cold Environment

Malaysia has restricted the use of biodiesel blends to B7 in the highlands due to challenges related to cold flow operability, while B10 and B20 are used in the lowlands. This study evaluated the performance and emissions of a light-duty, 4-cylinder Euro III turbocharged common rail direct injection diesel vehicle using palm biodiesel blends (B10, B20, and B30) at speeds of 60, 80, and 100 km/h under simulated cold temperatures of 10, 15, and 20°C in a controlled cold chamber. The combustion of B10 and B20 in the diesel engine showed enhancements in power and torque of 3.9% and 4.6%, respectively, compared to Euro 2M (B7) diesel. These improvements are likely the result of the synergistic effects of the enriched oxygen levels in biodiesel and the increased density of cold air, which enhance combustion efficiency. CO2 emissions decreased by 1.5%, 4.3%, and 11.2% with the use of B10, B20, and B30 fuels, respectively. NOx emissions decreased as biodiesel content increased at 10 and 15°C; however, the emissions increased by 17.6% and 38.2% for B20 and B30, respectively, in comparison to B10 at 20°C. B20 demonstrated good engine performance and emissions at 15°C, with improvements of 1.3% in power and 3.7% in torque, which compensated for a 3.2% increase in fuel consumption, and there were reductions of 8.9% in NOx emissions and 0.9% in CO2 emissions compared to B7 diesel. Palm biodiesel blends ranging from 7 wt.% to 20 wt.% are capable of withstanding the moderate cold ambient temperatures of the highlands without compromising engine operation.

Analyzing the impact of injection timing variations on the performance of multi-cylinder CNG direct injection spark-ignition engine

Abstract Objective: This study investigates the impact of Compressed Natural Gas (CNG) injection timing on the performance of a retrofitted CNG Direct Injection (CNG-DI) engine. The aim is to understand how varying injection timing affects key performance metrics such as torque, power, thermal efficiency, and fuel consumption in CNG-DI engines, providing insights for system optimization.
Methods: A 1298 cc, four-cylinder, four-stroke spark ignition engine with a compression ratio of 9 was retrofitted for CNG-DI operation. Modifications included a redesigned cylinder head for high-pressure injectors, controlled by a programmable gas ECU. The engine was tested with three injection timings: Early Injection (EI) at 230° BTDC, Optimal Injection (OI) at 180° BTDC, and Late Injection (LI) at 130° BTDC. Performance, Emission and Combustion parameters were evaluated across engine speeds from 1000 to 3100 rpm.
Results: Late Injection (LI) timing improved torque, power, BMEP, thermal efficiency, and volumetric efficiency by 4-16% within the 1000-2200 rpm range, attributed to better combustion dynamics. Optimal Injection (OI) timing achieved 4-12% higher performance in the 2500-2800 rpm range due to improved mixture formation. Early Injection (EI) timing resulted in 3-8% improvements at speeds above 2800 rpm, driven by faster combustion and increased peak power.
Conclusion: This study highlights the crucial role of injection timing in optimizing CNG-DI engine performance: Late Injection improves fuel efficiency at lower speeds, Optimal Injection enhances thermal efficiency at mid-range RPMs, and Early Injection maximizes power at higher RPMs. However, the study is limited by its focus on a single engine configuration and does not consider emissions or Life Cycle Assessment (LCA). Future research should investigate the environmental impact of injection timing through LCA and assess the long-term durability of engine performance.

Effects of injection timing on combustion and mixture formation of a methanol direct injection engine equipped with a small volume passive pre-chamber

The pursuit of high efficiency and cleanliness has always been the focus of engine research. As one of the most promising low-carbon renewable alternative fuel, methanol has gained increasing attention in engine applications. Inspired by the advantages of gasoline direct injection (GDI) in fuel economy, methanol direct injection (MDI) engine has also become a research hot spot. Similar to GDI, the mixture distribution is crucial for MDI engines, especially in the late injection stratified operation mode, an unreasonable mixture distribution of rich and lean regions will result in slow and incomplete combustion, or even flame quenching. Due to the characteristics of multi-point ignition and the high ignition energy, pre-chamber jet flame ignition has the potential to effectively enhance combustion. In this paper, the effect of injection timing on combustion characteristics in a methanol direct injection engine equipped with a small volume pre-chamber are studied experimentally. The mixture formation processes in both the main-chamber and the pre-chamber at different injection timings were also explored through simulations. The research findings indicated that the engine exhibits optimal power performance at the injection timing of − 270 °CA ATDC (after top dead center), primarily attributed to the enhanced volumetric efficiency and improved mixture homogeneity. However, the mixture concentration in the pre-chamber is leaner, resulting in the longest ignition delay period. When the injection timing is located on the middle state of the intake stroke, specifically − 210 °CA ATDC, the ignition delay period is the shortest, indicating that the mixture concentration and temperature in the pre-chamber are conducive to the flame kernel formation and flame propagation. In addition, the volumetric efficiency of this injection case is maximized due to the combined effects of spray-wall interaction, spray-air interaction, and the flow field. When injection occurs on compression stroke, the mixture concentration in the pre-chamber is higher; however, there exists a significant and discontinuous concentration gradient in the main-chamber, which limits the enhancement of the flame propagation speed and the combustion efficiency, especially for − 120 °CA ATDC injection case, the engine exhibits longest combustion duration and the lowest IMEP. The conclusions can provide theoretical basis and empirical data support for enhancing the combustion of methanol direct injection engines equipped with passive pre-chambers.

Combustion and Emission Characteristics of Methanol–Diesel Dual Fuel Engine at Different Altitudes

Currently, in the two technological approaches for using diesel pilot injection to ignite methanol and partially substituting diesel fuel with methanol, neither can fully achieve carbon neutrality in the context of internal combustion engines. Compression-ignition direct-injection methanol marine engines exhibit significant application potential because of their superior fuel economy and lower carbon emissions. However, the low cetane number of methanol, coupled with its high ignition temperature and latent heat of vaporization, poses challenges, especially amidst increasingly stringent marine emission regulations. It is imperative to comprehensively explore the impacts of the engine geometry, intake boundary conditions, and injection strategies on the engine performance. This paper first investigates the influence of the compression ratio on the engine performance, subsequently analyzes the effects of intake conditions on methanol ignition characteristics, and finally compares the combustion characteristics of the engine under different fuel injection timings. When the compression ratio is set at 13.5, only an injection timing of −30 °CA can initiate methanol compression ignition, but the combustion is not ideal. For compression ratios of 15.5 and 17.5, all the injection timings studied can ignite methanol. Reasonable increases in the intake pressure and intake temperature are beneficial for methanol compression ignition. However, when the intake temperature rises from 400 K to 500 K, a decrease in the thermal efficiency is observed. Particularly, at an injection timing of −30 °CA, both the peak cylinder pressure and peak cylinder temperature are higher, the ignition occurs earlier, the combustion process shifts forward, and the combustion efficiency and indicated thermal efficiency are at higher levels. Furthermore, the overall emissions of NOX, HC, and CO are relatively low. Therefore, selecting an appropriate injection timing is crucial to facilitate the compression ignition and combustion of methanol under low-load conditions.

Numerical one-dimensional investigation on GDI engine using LPG,water-ethanol-gasoline micro-emulsion fuel and Hydrogen, for net zero carbon emissions

The current issue of pollution has prompted researchers to reconsider emission control measures, leading many countries to focus on the development of Euro VII Emission Regulations. The present study aims to contribute to this goal by exploring ways to reduce emissions while improving performance. To achieve this, one-dimensional numerical simulations were conducted using AVL Boost software to predict the emission characteristics and performance of a gasoline direct injection (GDI) engine fuelled with LPG, water-gasoline emulsion, and hydrogen in dual fuel mode. Specifically, the study compares the performance of 100 % LPG and 100 % hydrogen with that of a water-based gasoline emulsion fuel consisting of 90 % gasoline, 8 % ethanol, and 2 % water (H2O 2 %). The geometrical properties of the GDI engine were kept consistent with those of the test rig. The results obtained from the numerical simulations demonstrate that the use of 100 % hydrogen and 100 % LPG significantly enhances the overall performance of the engine. Notably, hydrogen fuel exhibits a 50 % increase in brake power compared to the water–ethanol-gasoline emulsion fuel. Furthermore, 100 % LPG fuel generates 33 % more power than the emulsion fuel. Additionally, Hydrogen demonstrates a 30 % reduction in fuel consumption compared to micro emulsion fuel, while LPG exhibits a 15 % decrease in fuel usage compared to micro emulsion fuel. The study also examines the emission characteristics of the alternative fuels. Once again, 100 % hydrogen fuel proves to be the most efficient, producing zero carbon-based emissions. In comparison, 100 % LPG fuel emits 20 % less carbon monoxide and 15 % less hydrocarbon than the emulsion-based fuel.

Gas jet structure effects on fuel concentrations and flames in a hydrogen low-pressure direct-injection spark-ignition engine

This study aims to find the impact of the nozzle shape of a side-mounted, 3.5-MPa pintle injector on hydrogen concentration and flame development in a low-pressure direct-injection spark ignition (H2LPDI) engine. To this end, endoscopic high-speed imaging of gas jet laser shadowgraph and flames as well as spark-induced breakdown-spectroscopy (SIBS) method are applied to one of the inline four cylinders of H2LPDI engine. Two engines with endoscopic access are used: one motored engine for high-speed laser shadowgraph imaging of gas jet development and the other combustion engine for SIBS-based spark gap [Formula: see text] measurements and high-speed hydrogen flame imaging. The gas jet visualisation showed that a nozzle with a narrower jet spreading angle leads to more turbulent jet boundaries and the jet axis being directed more towards the piston. Due to higher axial momentum, the narrower spreading angle nozzle also caused enhanced jet penetration across the in-cylinder tumble flow. This jet development pattern resulted in locally leaner hydrogen mixtures near the centrally mounted spark plug at the time of ignition, evidenced by a higher difference between spark gap λ and global λ. As a result, the flame size was measured smaller at any fixed combustion stage. For both nozzle types, the injection timing was also varied between 150 and 120 °CA bTDC but there was no significant difference measured in spark gap [Formula: see text] and flame size compared to that associated with the nozzle type.

Acceleration of Modeling Capability for GDI Spray by Machine-Learning Algorithms

Cold start causes a high amount of unburned hydrocarbon and particulate matter emissions in gasoline direct injection (GDI) engines. Therefore, it is necessary to understand the dynamics of spray during a cold start and develop a predictive model to form a better air-fuel mixture in the combustion chamber. In this study, an Artificial Neural Network (ANN) was designed to predict quantitative 3D liquid volume fraction, liquid penetration, and liquid width under different operating conditions. The model was trained with data derived from high-speed and Schlieren imaging experiments with a gasoline surrogate fuel, conducted in a constant volume spray vessel. A coolant circulator was used to simulate the low-temperature conditions (−7 °C) typical of cold starts. The results showed good agreement between machine learning predictions and experimental data, with an overall accuracy R2 of 0.99 for predicting liquid penetration and liquid width. In addition, the developed ANN model was able to predict detailed dynamics of spray plumes. This confirms the robustness of the ANN in predicting spray characteristics and offers a promising tool to enhance GDI engine technologies.

Microscopic and macroscopic analysis of the flashing and non-flashing ethanol blended fuel for the direct injection sprays

Gasoline direct injection (GDI) engines offer improved fuel atomization, performance, and reduced emissions. Flash boiling in GDI engines enhances atomization. This study investigates ethanol-gasoline blended fuel spray using a single-hole direct atomizer. Micro- and macroscopic experimental analysis was conducted using a Galilean beam expander and Nd: YAG laser. The current study focused on initial, quasi-steady, and post-injection stages of flashing and non-flashing sprays. The transitional flashing jet exhibited various shapes similar to non-flashing sprays. An orbicular-shaped jet was observed during flare flashing at 0.03 MPa chamber pressure and 363 K fuel temperature. It exhibits rapid axial momentum, resulting in a Reynolds number of 8.0 x 104, 1.3 and 2.15 times higher than the transitional and non-flashing sprays. Additionally, it has an estimated nucleation rate of 3.22 x 10-2 m-3s−1 using classical nucleation theory, which is 10 times higher than the transitional flashing, leading to improved atomization. However, spray collapse was observed under flare flashing with reduced chamber pressure, attributed to local condensation and subsequent pressure drop in spray core. Under flare flashing at a fuel temperature of 403 K, the Ohnesorge number is 2.95 x 10-3, which is 0.8 times and 0.7 times lower than the fuel at 383 K and 363 K, respectively. The nucleation rate for flare flashing increases with higher fuel temperature, leading to improved atomization and a reduced likelihood of spray collapse. Post-injection spray structures in the near-nozzle show a transition from coarse to fine and dilute to densely populated, with changes in degree of superheating.

Investigations of diesel and natural gas injection interaction on combustion characteristics of a high-pressure direct-injection dual-fuel engine based on large eddy simulation

HPDI (high-pressure direct-injection) with pilot ignition is modern technology developed for heavy-duty natural gas engines. The dynamics of coherent flow structures due to diesel and natural gas jet play a significant role on ignition characteristics. In this study, a large eddy simulation (LES) framework coupled with chemistry solver is conducted for three-dimensional modelling of the thermal process of a HPDI engine. By integrating the Dynamic Mode Decomposition (DMD) algorithm, the break-up and attenuation process of unstable flow structures accompanied by different scale vortex formation and dissipation is able to be effectively demonstrated from fuel jet. The prime in-cylinder flow field structures from natural gas injection to its ignition is characterized by the vortex entrainment phenomenon resulting from the impingement between the natural gas jet and active products from diesel combustion. This phenomenon leads to enhanced heat transfer and exchange of active radicals by which the ignition of the natural gas is therefore facilitated, especially when angle β (the intersection angle between diesel and nature gas jet) is decreased. Moreover, the present study extends the ability of reaction-rate based global pathway analysis to evaluate the reactivity of OH additions to CH4/air mixture. In summary, the interactive dual fuel turbulent combustion process of the HPDI engine is theoretically elucidated, wherein the synergetic kinetics of vortex entrainment-mixing and chemical reaction facilitate the ignition of low reactivity natural gas.

Hydrogen-enriched lean-burn strategy for gasoline direct injection engine utilizing non-thermal plasma fuel reformer

The objective of the task is to sustain and enhance combustion stability at the extension of lean limit of customized Gasoline Direct Injection (GDI) Engine with the supplementation of Hydrogen Rich Gas (HRG) and hydrogen. HRG was supplemented from the on board non thermal Plasma Fuel Reformer (PFR) and hydrogen from the bottled storage through integrated gas control device to the GDI engine. The gas constituents of PFR was theoretically arrived from thermodynamic combustion equations to determine energy based fuel proportion in the ternary fuel injection system. Binary fuel mixture of HRG and hydrogen 10%, 18%, 30% of energy based proportion with gasoline were experimented on test engine. The impact of discrete and binary fuel mixture with gasoline at Stoichiometric Fuel Air ratio was observed and extended baseline equivalence ratio until misfire of the ternary fuel air mixture was occurred. Apart from significant improvement of performance the addition gaseous mixture increases oxides of nitrogen marginally. From the perspective it was noticed that combustion products exhibit better heat transfer out of cylinder at the Maximum Brake Torque Timing (MBT). This was attributed to higher combustion temperatures and improved quenching distances which in turn increased thermal efficiency against the specified equivalence ratio. However retarding MBT suppresses oxides of nitrogen and continued to increase thermal efficiency. It was concluded that lightning fast burn speed, fine fuel atomization of 10% mass based hydrogen and HRG 18%combination fraction increase engine thermal efficiency while decreasing NOx emission and alleviate HC trade-off characteristics.

Effect of engine parameters on the mixture distribution, performance and emission characteristics of a gasoline direct injection engine with baffles – A numerical analysis

Baffles inside the combustion chamber of internal combustion (IC) engines improve in-cylinder mixture distribution, performance, and emission characteristics. However, the effect of engine operating parameters on these aspects of the engine with baffles (EWB) remains underexplored. In this study, using computational fluid dynamics (CFD), the effects of fuel injection pressure (FIP), engine speed and load in a spray-guided, gasoline direct injection engine (GDI) are analysed and compared with the conventional engine. For the analysis, injection pressures of 30, 50, 80, and 120 bar; engine speeds of 1000, 2000, and 3000 rev/min.; and overall equivalence ratios of 0.7, 0.9, and 1.2 are considered, keeping the fuel injection timing constant. Results show that, EWB outperforms the conventional engine under various conditions considered. Also, it is found that the performance of EWB at an FIP of 30 bar is comparable to that of the base engine at an FIP of 80 bar. Additionally, the EWB exhibits better thermal efficiency across all the engine speeds and load conditions. Moreover, the HC and CO emissions of the EWB are found to be lower in most engine operating conditions. However, NOx emissions are marginally higher than those of the base engine.

Optimization of combustion chamber geometry for a two-stroke spark-ignited direct-injection opposed-piston rod-less aviation kerosene engine

Spark-ignited direct-injection opposed-piston rod-less kerosene engines are highly suitable for small and medium-size unmanned aerial vehicles (UAVs) because of the high power-to-weight ratio, self-balancing ability, and safety of such engines. The design and optimization of combustion systems are crucial for power, fuel economy, and knock control. To meet the increasing demand for UAV power systems and fill the research void in this area, reported here for the first time are the design and optimization of a swirl-wall-guided combustion system including the spray pattern and pit structure on the top surface of the piston, with the dynamic, fuel economy, and knock intensity as the evaluation indicators. The results indicate that the spray pattern mainly affects the fuel escape rate and inhomogeneity. After it is injected into the pit, the fuel is guided to the combustion chamber by the steering role of the guide arc. If the spray drop point is located away from the pit, it leads to increased fuel escape rate and inhomogeneity. The turbulent kinetic energy in the spark-plug zone decreases as the pit diameter decreases, fluctuating by 48 %, while the average value remains relatively constant. The distribution is influenced primarily by the enveloping effect of the pit structure on the airflow. Under low-speed conditions, as the pit diameter decreases, the ignition delay period increases and then decreases, and the combustion duration decreases monotonically. The fluctuation of indicated power is relatively small (2.64 %), and the fuel escape rate decreases monotonically, resulting in the same variation pattern of indicated specific fuel consumption (ISFC). When the pit diameter is 43 mm, the fuel escape rate and ISFC reach their lowest values. Knock combustion near the wall is influenced mainly by two factors: the temperature rise rate and the flame propagation speed. The temperature rise rate increases significantly with decreasing pit diameter. When the pit diameter is less than 50 mm, knock combustion begins to occur. Under high-speed equivalent combustion conditions, as the pit diameter decreases, the indicated power changes by 5.21 %, and the ISFC decreases monotonically.

Investigation of fuel temperature and injection timing effects on ammonia direct injection in an optical engine

This work investigates the effects of fuel temperature and injection timing on ammonia direct injection in an optical engine using a multi-hole injector. Flash-boiling may occur over various engine-relevant conditions due to ammonia’s high vapor pressure. This phenomenon impacts spray characteristics and, in severe cases, facilitates cavitation inside the nozzle. Both fuel temperature and injection timing (i.e., ambient conditions during injection) impact the intensity of flash-boiling during fuel injection. Therefore, this work varies fuel temperature (from 320K to 388K) and injection timing (from −60CADaTDC (crank angle degrees after top dead center) to −6CADaTDC) to assess their impact on injection mass flux, discharge coefficients, and macroscopic spray characteristics using an ammonia injection pressure of 200bar. For this purpose, the injection mass is measured by analyzing exhaust gas compositions during engine operation with ammonia injections but without combustion. In addition, diffuse background illumination (DBI) images capture the liquid phase of the fuel spray to characterize spray behavior. The findings reveal that increasing fuel temperature decreases ammonia’s injection mass by up to 12.8% but has little impact on discharge coefficients for late injection timings and high in-cylinder pressures. However, discharge coefficients decrease by up to 17.4% (from 0.58 to 0.48) for early injection timings if fuel temperatures are high. The individual sprays of the 6-hole GDI injector may collapse into a uniform spray at high-density conditions without flash-boiling or under strongly flash-boiling conditions. The findings clarify the impact of ammonia’s high vapor pressure on injection mass and prove the relevance of different spray collapse mechanisms in ammonia direct injection engines.

Ammonia diffusion combustion and emission formation characteristics in a single cylinder two stroke engine

Liquid ammonia diffusion combustion (LADC) is an effective approach to achieving high ammonia energy ratio (AER) and combustion efficiency in engines. However, there is a lack of simulation studies of LADC mode in ammonia/diesel dual direct injection engines. To address this gap, the study develops a numerical model based on an independently modified marine two-stroke engine. This model analyzes the combustion performance of ammonia in LADC mode and the pollutant generation mechanisms in LADC mode across various AER conditions. The findings indicate that in the LADC mode, the liquid phase ammonia spray exhibits a concentrated distribution area, facilitating thorough combustion of ammonia fuel. The diesel mixture and flame are entrained into the liquid phase ammonia spray, facilitating multi point ignition. This process notably enhances combustion speed, thereby reducing overall combustion duration. In comparison to pure diesel combustion, soot emissions are reduced by 99 % under the LADC mode, and CA90 advanced by 11.8 °C A. In addition, when the AER range is from 50 % to 70 %, the engine exhibits favorable combustion and emission characteristics. By appropriately adjusting the liquid ammonia injection quantity, the indicated thermal efficiency improves by 10.7 %, the equivalent indication specific fuel consumption decreases by 13.9 %, and the emission such as NOx and soot can be also reduced effectively.

Design and optimization of combustion chamber geometry and fuel spray targeting of a natural gas/biodiesel dual direct injection engine

In pilot fuel-ignited stratified premixed natural gas (NG) engines, the combustion chamber geometry significantly influences the distribution of NG. Meanwhile, the fuel spray targeting affects the dynamic distribution of the pilot fuel and NG mixture, thereby exerting a crucial impact on subsequent combustion. This study numerically investigated the coupling effects of combustion chamber geometry and fuel spray targeting on the performance of a NG/biodiesel dual direct injection engine, aiming to optimize these parameters. Three combustion chambers (double-lip, reentrant, and hemispherical) were constructed for comparison with the original open crater design. Based on the spray targeting of NG, the NG injection was categorized into three cases (A, B, and C) corresponding to NG injection into the squish region, the piston throat, and the piston bowl, respectively. The results indicate that the effect of combustion chamber geometry on NG distribution varies depending on the NG injection situation, with the impact being more pronounced in Cases B and C than in Case A. The spray targeting of biodiesel not only affects the biodiesel-NG mixing but also changes the ignition position. It is found that the variation of biodiesel ignition angle (BIA) in Case C has a much smaller impact on engine performance compared to Cases A and B. The double-lip combustion chamber with a large BIA is more favorable for Cases A and B, whereas the hemispherical combustion chamber with a small BIA achieves the best performance in Case C.

A novel valve strategy for particulate matter reduction in a gasoline direct injection engine operated at cold conditions

In this study, we proposed a novel intake strategy to reduce Particulate matter (PM) emissions from gasoline direct-injection (GDI) engines during cold-start conditions emissions. This strategy is characterized by generating strong intake turbulence and low in-cylinder pressure during fuel injection through delayed intake valve opening, which theoretically promotes fuel atomization and fuel-air mixture, thereby suppressing PM formation during combustion. Experiments were conducted on a single-cylinder GDI research engine, operating at 1500 rpm, 3, 6, and 8 bar IMEP, and stoichiometric air-fuel ratio conditions with low coolant and lubricant temperatures to experimentally demonstrate the effectiveness of the proposed valve strategy in reducing PM emissions. Benchmark tests were performed using an intake camshaft with intake valve opening (IVO) at −13 °aTDC and intake valve closing (IVC) at 227 °aTDC. The novel strategy uses an intake camshaft with very late IVO at 66 °aTDC and IVC at 226 °aTDC. Two injection pressures (Pinj = 100/200 bar) were used to evaluate the pressure requirement for achieving low PM emissions with both strategies. Start of injection was swept and optimized to match the valve strategy. The results showed that the novel valve strategy leads to a 50%–90% reduction in particle number and mass emissions in cold-start conditions, and a lower injection pressure requirement to achieve comparable particle number and mass emissions compared with the normal one. For the novel valve strategy, the fuel impingement with early injection timings is largely mitigated, and thus an early injection timing shortly before the IVO is recommended.

A novel approach of in-cylinder NOx control by inner selective non-catalytic reduction effect for high-pressure direct-injection ammonia engine

As an efficient hydrogen carrier and carbon-free fuel, ammonia shows great promise in realizing zero-carbon propulsions. However, challenges such as poor ignition stability, low combustion efficiency, and fuel-NOx emissions are yet to overcome. In this paper, the high-pressure direct-injection ammonia/diesel dual-fuel combustion mode (HPDF) with post injection strategy is proposed as a solution. The study reveals that HPDF combustion mode enables in-cylinder reduction of NOx, which is attributed to the selective non-catalytic reduction (SNCR) reaction. The results uncover that NH2, NH, and N radicals have a significant reducing effect on NO and NO2, while N2O serves as an important byproduct of the reduction reactions. Subsequently, the generated N2O can be further reduced to N2 through the involvement of O, H, and OH radicals. Building upon these findings, an innovative ammonia post injection method for reducing NOx emissions is explored. The post injection strategy effectively reduces the NOx emissions with only a minor decrease in indicated thermal efficiency, but an over-delayed post injection could also cause significant increase in N2O and unburned NH3 emissions. A post injection proportion of 20%-30% with appropriate post injection timing is found to achieve desired emission reduction. Overall, the HPDF combustion mode is a promising solution for ammonia engine, due to the high thermal efficiency and low nitrogen oxide emissions, as well as the ability to further reduce the NOx emissions through ammonia post injection strategy.

Hydrogen enrichment in methanol SI engine at varying injection timing during compression stroke

This study investigates the effect of hydrogen enrichment in a direct-injected methanol-fuelled SI engine, with combustion and emission performance analysed by varying the methanol injection timing from 150° to 60° CA bTDC. A three-dimensional computational fluid dynamic model of the hydrogen-enriched methanol engine was developed to predict the engine performance, in-cylinder, and emission characteristics. The numerical model was solved using three-dimensional Reynolds-Averaged Navier Stokes, the RNG k-epsilon model for turbulence, the O'Rourke and Amsden sub-model for heat transfer, the extended Zeldovich mechanism for nitric oxide emissions, and the Hiroyasu-NSC model for soot emissions. The results indicated that retarding the injection timing resulted in a decrease in the indicated specific CO and soot emissions along with a rise in the indicated specific NOx emissions. Furthermore, hydrogen enrichment with methanol enhanced the hydroxyl radical concentration, reduced the combustion duration, reduced also the indicated specific CO and soot emissions while increasing the indicated specific NOx emissions. The study indicates that hydrogen enrichment could extend the late injection timing limit of methanol by enhancing fuel-air mixing, which improves and controls the combustion process more effectively.

Experimental analysis and optimization of the variable valve timing on attaining high efficiency with low NOx emission of a direct-injected hydrogen engine

The direct-injection hydrogen engine (DI-H2ICE) has demonstrated zero carbon emissions with high brake thermal efficiencies (BTE). Due to the high stoichiometric air–fuel ratio of hydrogen, with a lean burn strategy the gas exchange process of a hydrogen engine is different to a gasoline engine, and the valve timing controlling strategy requires reinvestigation. In this research, the optimal variable valve timing (VVT) is investigated in a 2.0 L DI H2ICE. The intake and exhaust valve timing controlling strategies are analyzed experimentally over the whole operating map. A multi-indicator decision-making method is applied to determine the entropy weight of BTE and NOx emissions. Results indicate that BTE greatly benefits from advanced intake valve timing, and exhaust valve timing affects BTE through pumping losses. Advanced intake and exhaust valve timings are employed in the hydrogen engine to enhance the BTE until the NOx emissions rise rapidly at high loads. The retarded exhaust valve timing helps reduce NOx emissions and avoid the risk of abnormal combustion at high loads. Therefore, earlier IVO and later EVC are applied simultaneously for DI-H2ICE compared to the gasoline engine. A maximum power of 124.8 kW at an engine speed of 4500 rpm and a BTE of 42.57 % is achieved with optimized VVT. Furthermore, NOx emissions are controlled to under 20 ppm over nearly half of the engine operating map. The conclusions are valuable in the development of high-performance H2ICEs, the numerical simulation studies, and hydrogen fuel applications.

Study on laminar combustion characteristics and the optimization of the coupling mechanism in a mixture of propanol and gasoline

When both isopropanol and n-propanol are incorporated, the utilization of propanol as a fuel substitute (or a gasoline additive) presents promising potential for enhancing the combustion efficiency and thermal performance in compact, turbocharged, direct-injection gasoline engines upon blending. However, the complexity of the laminar combustion behavior of propanol-blended gasoline has yet to be fully investigated, as current coupling mechanisms are insufficiently sophisticated to precisely mirror the complex experimental conditions.This study establishes a testbed specifically designed for measuring laminar burning velocity (LBV) using the heat flux method. This setup is employed to measure the LBV of pure n-heptane and isooctane, as well as the LBV of the gasoline surrogate fuel TRF with two distinct blend ratios. Additionally, it measures the LBV of propanol and its blends with TRF. The research findings reveal that isooctane demonstrates a heightened sensitivity to fuel preheating temperature, whereas the toluene proportion in TRF fuels exerts the most pronounced influence on combustion behavior. At an equivalence ratio of 1.1, the LBV of n-propanol differs from that of its isomer, isopropanol, by 4.65 cm/s. Notably, the LBV exhibits a discernible upward trend, corresponding to the increasing proportion of toluene in the blended fuel. Furthermore, there is a pronounced distinction in LBV among the propanol isomers, with blended TRF occupying an intermediate position between pure propanol and TRF. After the enhancement of the mechanism based on experimental benchmarks of LBV, a rigorous validation process demonstrated a substantial improvement in the alignment between simulated outcomes and empirical LBV measurements.