Direct Injection Internal Combustion Engines Research Articles

Toward High-Efficiency and Low-Emissions Hydrogen Direct Injection Internal Combustion Engine: Pre-Chamber Turbulent Jet Ignition

ABSTRACT Hydrogen internal combustion engine (HICE) holds significant promise for transitioning to clean fuels within the transportation field. This research investigates the adaptability of pre-chamber turbulent jet ignition (TJI) in direct injection (DI) HICE, focusing on addressing challenges such as reduced flame speed under lean-burn strategy and high NOx emissions during high-efficiency operation. Using a 3D CFD model of a DI HICE, we explore the impact of different ignition modes on mixing, combustion, and NOx emissions. Our findings reveal that the passive pre-chamber mode leads to a modest improvement in thermal efficiency and a reduction in NOx emissions compared to the spark ignition (SI) mode. In contrast, the active pre-chamber mode, characterized by a faster flame velocity, enhances indicated thermal efficiency (ITE) by about 2% compared to other ignition modes. We identify an optimal injection strategy for the pre-chamber, involving the injection of 0.3 mg of hydrogen. Deviations from this hydrogen quantity adversely reduce the thermal efficiency. Moreover, advancing injection timing promotes fuller mixing at higher turbulent kinetic energy, resulting in faster flame propagation albeit with a marginal rise in NOx emissions. Adjusting the equivalence ratio leads to an extension of the lean burn limit to the equivalence ratio of 0.25, while still achieving efficient combustion with ITE exceeding 49% at equivalence ratios of 0.3 or higher. Ultimately, we demonstrate the attainment of high-efficiency and low-emission combustion, with ITE surpassing 50% and NOx emissions falling below 80 ppm.

A Numerical Simulation of Mixture Formation in a Hydrogen Direct-Injection Internal Combustion Engine

Direct-injection technology applied in hydrogen internal combustion engines can effectively prevent backfire, thereby improving the engine performance. Nonetheless, optimizing the injection strategy is highly intricate, requiring a comprehensive understanding of the hydrogen–air mixture formation process inside the cylinder. In this study, a simulation of hydrogen–air mixture formation was systematically conducted in a hydrogen direct-injection internal combustion engine using three-dimensional computational fluid dynamics (CFD) software. Under rated conditions, the influence of the nozzle hole number, injection direction, injection timing, and combustion chamber geometry on the mixture formation was analyzed from the perspectives of flow state and mass transfer. The results indicate that more nozzle holes would lead to more significant non-uniformity of the mixture, mainly due to the Coanda effect. The normalized standard deviation (NSD) of a six-hole nozzle design is 0.3495, which is higher than the NSD of all the single-hole nozzle conditions. By changing the hydrogen injection timing from −144 °CA to −136 °CA, the non-uniformity coefficient of the mixture is little affected, while notable differences in the distribution of the mixture are observed. The appropriate injection directions and optimized combustion chamber geometries could also help to effectively organize the in-cylinder flow, significantly improving the uniformity of the in-cylinder mixture and reducing the likelihood of abnormal combustion events.

A Comparison of Well-to-Wheels Energy Use and Emissions of Hydrogen Fuel Cell, Electric, LNG, and Diesel-Powered Logistics Vehicles in China

Global energy and environmental issues are becoming increasingly serious, and the promotion of clean energy and green transportation has become a common goal for all countries. In the logistics industry, traditional fuels such as diesel and natural gas can no longer meet the requirements of energy and climate change. Hydrogen fuel cell logistics vehicles are expected to become the mainstream vehicles for future logistics because of their “zero carbon” advantages. The GREET model is computer simulation software developed by the Argonne National Laboratory in the USA. It is extensively utilized in research pertaining to the energy and environmental impact of vehicles. This research study examines four types of logistics vehicles: hydrogen fuel cell vehicles (FCVs), electric vehicles, LNG-fueled vehicles, and diesel-fueled vehicles. Diesel-fueled logistics vehicles are currently the most abundant type of vehicle in the logistics sector. LNG-fueled logistics vehicles are considered as a short-term alternative to diesel logistics vehicles, while electric logistics vehicles are among the most popular types of new-energy vehicles currently. We analyze and compare their well-to-wheels (WTW) energy consumption and emissions with the help of GREET software and conduct lifecycle assessments (LCAs) of the four types of vehicles to analyze their energy and environmental benefits. When comparing the energy consumption of the four vehicle types, electric logistics vehicles (EVs) have the lowest energy consumption, with slightly lower energy consumption than FCVs. When comparing the nine airborne pollutant emissions of the four vehicle types, the emissions of the FCVs are significantly lower than those of spark-ignition internal combustion engine logistics vehicles (SI ICEVs), compression-ignition direct-injection internal combustion engine logistics vehicles (CIDI ICEVs), and EVs. This study fills a research gap regarding the energy consumption and environmental impact of logistics vehicles in China.

Co-optimizing Engine Hardware and Fuel Chemistry for Improving Thermal Efficiency and Reducing Pollutant Emissions of Gasoline Fueled Direct Injection Internal Combustion Engines

Co-optimizing Engine Hardware and Fuel Chemistry for Improving Thermal Efficiency and Reducing Pollutant Emissions of Gasoline Fueled Direct Injection Internal Combustion Engines

The Influence of Nonthermal Plasma Technology on Oxidation Characteristics of Soot Operated on Direct Injection Internal Combustion Engines

The combination of porous material with nonthermal plasma (NTP) technology to reduce the amount of particulate matter emitted from a direct-injection compression-ignition engine was investigated in this study. The investigation aimed at regulating particulate matter under long-term operation. A porous materials filter thickness of 4 mm was installed in the NTP reactor. The common rail diesel engine was fueled with 7%-vol biodiesel fuel (B7), and the experiment was carried out at steady-state conditions at 2000 rpm and indicated mean effective pressure (IMEP) of 6 bar. The effects of NTP high-voltage discharge (e.g., 2, 4, 5, 6, 8, and 10 kV) and the porous filter thickness (e.g., 0, 2, 4, and 6 mm) on particle number size distributions were examined. The protype of combine porous filter and NTP illustrated good particulate removal (>70%) operated with a thickness of 4 mm of porous materials filter and a high voltage of 6 kV under the same power rating.

The Mechanism of Particle Formation in Non-Premixed Hydrogen Combustion in a Direct-Injection Internal Combustion Engine

There is a widely spread public and expert opinion that hydrogen combustion is a pathway for eliminating the formation of carbon-based pollutants, which produces near-zero-emissions. However, our studies show that non-premixed hydrogen combustion in engines may result in an enhanced particles formation, which is substantially higher than that stemming from hydrocarbon fuel combustion. This discovery contradicts all previously published data on particle formation in hydrogen combustion. We have accomplished an interlinked series of fundamental and engine studies enabling us to understand the physical reasons behind this apparent discrepancy and identify the mechanism governing particle formation in hydrogen combustion. The latter in non-premixed hydrogen burning is a result of a combined influence of the hydrogen low flame quenching distance, intensifying lubricant evaporation, and the gasdynamic interaction between the lubricant vapor and the fuel core-jet. This interaction results in the lubricant vapor entrainment into the chamber bulk with its subsequent combustion and particle formation.

Influence of the equivalence ratio on the knock and performance of a hydrogen direct injection internal combustion engine under different compression ratios

Hydrogen has become an ideal alternative fuel for internal combustion engines. However, with an increase in the equivalence ratio and compression ratio, knock combustion is more likely to occur, which limits its engineering application. In this study, the effects of the equivalence ratio on the knock under different compression ratios were studied through numerical simulation. The signal energy ratio (SER) were used to evaluate the knock onset (KO). The knock intensity (KI) and engine performance were compared and analyzed under different equivalence ratios and compression ratios. The results revealed that a high compression ratio can significantly amplify the effect of the equivalence ratio on combustion and knock. Under the compression ratio of 17.5, KI increases more quickly, with the constant equivalence ratio rise and is more sensitive to ignition timing with equivalence ratio increasing. For the compression ratio of 11, the ignition timing limited by knock is about 4°CA earlier than that of compression ratio of 17.5, and the engine performance is more stable in the low-knock zone. However, when KI exceeds 1 MPa, the power and ITE decreases 20.6% and 20.9% respectively.

Large-eddy simulation of methane direct injection using the full injector geometry

Understanding the mixing process of under-expanded gaseous-fuel jets from an outward opening injector is essential for developing Direct Injection (DI) internal combustion engines. This paper presents a Large-Eddy Simulation (LES) study of the DI of methane into a Constant Volume Chamber (CVC), considering the full, internal geometry of a prototype injector. Four cases at conditions relevant to Compressed Natural Gas (CNG) DI engines are investigated, with methane as a surrogate for CNG. A new post-processing method permits the 3D LES field to be projected into a 2D density gradient field that can be compared to a schlieren image. The LES results are then validated against high-speed, schlieren imaging experiments, demonstrating that the simulations are able to reproduce experimental trends. Three main regions of the external flow are observed: a recirculation zone just downstream of the injector tip, a stagnation zone and a far-mixing zone. The location of the stagnation zone increases as the CVC pressure decreases, consistent with a theory presented in the literature. The modelling of the full internal geometry of the injector leads to a determination of the injector pressure losses. Once the pressure loss within the injector is considered, a short version of the injector can reasonably represent the full injector for prediction of the external flow.

An experimental and numerical study of natural gas jets for direct injection internal combustion engines

Natural gas predominantly contains methane which is the cleanest burning hydrocarbon. It can be considered as the most promising alternative fuel that has the potential to replace gasoline and diesel. This is mainly due to wider availability, lower fuel price, favourable fuel properties and cleaner burning characteristics. Currently in all spark ignited CNG engines fuel is port injected that results in lower peak torque due to reduced volumetric efficiency. Direct injection can easily overcome this drawback and can match the performance levels of modern gasoline direct injection engines while emitting far less harmful pollutants. Gaseous direct injection produces highly diffusive under-expanded turbulent gaseous jets. In order to optimise mixture preparation and maximise combustion performance, the flow characteristics of gaseous jets need to be further understood and modelled. In this work, the fundamentals of gaseous flow from an outward opening direct injector is studied. Schlieren imaging is used at high spatial and temporal resolution to characterise the far-field jet growth. The nozzle in a typical outward opening direct injector has been found to produce a hollow conical jet at the beginning of injection which later collapses depending on the nozzle geometry and pressure ratio. The experimental data are used to validate a CFD model. A numerical investigation is carried out to predict the jet growth for different nozzle geometries and their effect on the jet characteristics such as mass flow rate, penetration and mixing is discussed.

Advantages and Disadvantages of Diesel Single and Dual-Fuel Engines

The pros and the cons of lean-burn, compression ignition (CI), direct injection (DI) internal combustion engines (ICE) are reviewed for transport applications. Fueling options considered include diesel only and dual-fuel applications with diesel and a gaseous fuel (CNG, LNG and LPG). CIDI ICEs have higher fuel conversion efficiencies than stoichiometric, spark ignition (SI) ICEs, whether DI or port fuel injected (PFI). However, diesel-fueled CIDI ICEs have higher particulate matter (PM) and NOx engine-out emissions. The tail-pipe NOx emissions in real-world driving of diesel-powered vehicles have been, in the past, above the limits requested over the simplified cold start driving cycles used for certification. This issue has recently been resolved. The newest diesel-powered vehicles are now compliant with new laboratory test cycles and real-world-driving schedules and have no disadvantages in terms of criteria air pollutants compared to older diesel vehicles, while delivering improvements in fuel economy and CO2 emissions. Dual-fuel CIDI ICEs offer the opportunity for enhanced environmental friendliness. Dual-fuel CIDI ICEs have lower engine-out NOx and PM emissions compared to diesel-only CIDI ICEs. The latest diesel-only vehicles and vehicles with dual-fuel ICEs deliver dramatic reductions in tail-pipe PM emissions compared to older diesel-only vehicles. Moreover, they deliver tail-pipe PM emissions well below the ambient conditions in most city areas that are highly polluted, thereby helping to clean the air. The diesel-fueled CIDI ICEs may be further improved to deliver better fuel economy and further reduced tail-pipe emissions. The dual-fuel CIDI ICE has more room for improvement to produce similar or better steady state and transient performance in terms of torque, power output and fuel conversion efficiency compared to diesel-fueled CIDI ICEs, while drastically reducing CO2 and PM tail-pipe emissions, and improving NOx tail-pipe emissions. This is due to the ability to modulate the premixed and diffusion phases of combustion with a second fuel that is much easier to vaporize and is less prone to auto-ignition. Further development of the fuel injection system for the second fuel will lead to novel dual-fuel CIDI ICE designs with better performance.

Particle emissions of direct injection internal combustion engine fed with a hydrogen-rich reformate

Thermochemical Recuperation is a promising waste heat recovery method that enables utilization of the engine waste heat together with onboard hydrogen production resulting in a significant improvement in thermal efficiency and a massive reduction in gaseous pollutants emission. However, an unexpectedly high particle emission level as compared to the gasoline-fed engine was measured despite the combustion of a hydrocarbon-free hydrogen-rich methanol steam reforming (MSR) products, containing 75% mol. H2 and 25% mol. CO2. In the existing literature, this phenomenon has not described yet.In this reported study, experiments are performed to investigate reasons of the elevated particle emissions by a direct injection spark ignition engine fed with MSR reformate, and results are compared with a baseline engine fed with gasoline at the same engine loads and speeds. Results of particle number concentration and size distribution measurements show that the total particle number concentration emission of engine fed with MSR reformate is 170% higher compared to gasoline. A direct experimental comparison between the port and the direct reformate injection performed on the same engine shows an increase in particles formation with a direct injection method. Based on these findings, several hypotheses are presented attributing to excessive lubricant involvement in the combustion process. The peculiarities specific for direct reformate injection that could result to the enhanced particles formation are jet – lubricated wall interaction, lubricant vapor entrainment into the reformate jet and shorter flame quenching distance of hydrogen compared to gasoline.

Effects study of injection strategies on hydrogen-air formation and performance of hydrogen direct injection internal combustion engine

Based on the dual challenges of the global energy crisis and environmental pollution, hydrogen has been recognized as an ideal alternative internal combustion engine (ICE) fuel. To improve the combustion efficiency of hydrogen direct injection ICE, we numerically analyzed the effects of different injection parameters, including injection timing, injection pressure, and dual injection, on the formation of a hydrogen-air mixture using the CONVERGE software from the perspective of mass transfer and flow state. It was determined that it is enough to set the injection timing to −88° after top dead center (ATDC) for both uniform mixture and desirable indicated thermal efficiency (ITE). However, when the injection timing is set to −43° ATDC, an acceptable ITE and effective combustion can be achieved by employing the “jet-room coordination” effect of the ω chamber. Injection pressure has a minimal effect on mixture formation and combustion. In contrast, the timing and mass fraction of secondary injection have a significant influence on tumble strength, which is a key factor for the mixture improvement.

Heating and evaporation of ethanol/iso-octane droplets considering non-ideal mixtures and finite rate transfer

In this paper, the heating and evaporation process of ethanol/iso-octane droplets is deeply investigated through analytical solutions and considering thermodynamic models for non-ideal mixtures. The study is based on the Effective Thermal Conductivity Model (ECM) and Effective Diffusivity Model (EDM), which take into account the finite thermal/mass diffusivities inside the droplets and also consider the effect of droplet internal recirculation. Three sets of cases are considered: ideal liquid and gas phases, non-ideal liquid and gas phases and ideal gas phase together with the non-consideration of the Poynting factor for the liquid phase. The activity coefficients for the non-ideal liquid phase are calculated through the UNIFAC model and the fugacity coefficients for the non-ideal gas phase are calculated from the Virial equation of state. A parametric study is performed with focus on relevant conditions to direct injection internal combustion engines, within an ambient pressure range from 1 to 20 bar, initial ambient gas temperature range from 453 K to 673 K and initial ethanol volume fraction inside the droplet varying from 0 to 1. The thermodynamic analysis of the mixture, the time evolution of the droplet surface temperature and mass fraction together with the droplet lifetimes are presented for several different conditions. The obtained results show that the effect of the non-ideality of both phases has a significant impact on the results when analyzing ethanol/iso-octane mixtures. From cases analyzed considering both phases as ideal mixtures the deviation of the droplet lifetime reached maximum values (in absolute value) of 15.6% at 1 bar, 10.5% at 10 bar and 14.9% at 20 bar and for the ideal gas approach (non-ideal liquid) the deviation reached maximum values (in absolute value) of 3.9% at 10 bar and 9.4% at 20 bar, when compared to the non-ideal approach. These deviations certainly can lead to significant deviations in the prediction of the mixture formation in direct injection engines.

Eccentric needle displacement effect on spray formation from a multi orifice diesel injector

As emission regulations becomes stringent, improving injection process in internal combustion (IC) engines, is one of the ways of enhancing combustion characteristics and reducing pollutants emissions. Hence in this study, the effect of on-axis and off-axis internal needle displacement on injection characteristics from a multi orifice injector, used in direct injection IC engines, were investigated and analyzed. Two stage off-axis needle movement was formulated for the investigation. The first stage was at the initial stage of the needle lift, where the needle continuously glides along the internal cone of the nozzle body, before it completely departs the body. The second stage was considered to be from the moment the needle completely departed the nozzle body. Two different direction of the two stage off-axis needle displacement, were analyzed and their effect on flow and spray characteristics compared to those from on-axis needle displacement. The results showed that, off-axis needle displacements in the immediate areas of the nozzle orifices, causes exponential increment in spray jet penetrations as compared to off-axis needle displacement around the maximum needle lift position. Also, the displacement at the early stages of injection, had more influence on the spreading angles of spray jets from the nozzle orifices than the needle displacement around full needle lift.

A New Fuel-Injection Mechatronic Control Method for Direct-Injection Internal Combustion Engines

Abstract In this paper, a novel fuel-injection mechatronic control method and system for direct injection (DI) internal combustion engines (ICE) is proposed. This method and system is based on the energy saving in a capacitance using DC-DC converter, giving a very fast ON state of the fuel injectors’ electro-magnetic fluidical valves without an application of the initial load current. A fuel-injection controller for the DI ICEs that provides a very short rising time of an electromagnet-winding current in an initial ON state of the fuel-injector’s electromagnetic fluidical valves, which improves a fuel-injection controller reliability and simplify its construction, is presented. Due to a number of advantages of afore -mentioned fuel-injection mechatronic control method and system, it may be utilised for the DI ICEs with fuel injectors dedicated to all types of liquid and/or gas fuels, for example, gasoline, diesel-oil, alkohol, LPG and NPG.

Near-azeotropic volatility behavior of hydrous and anhydrous ethanol gasoline mixtures and impact on droplet evaporation dynamics

After fermentation, the concentration of bioethanol is only 8–12 wt%. To produce anhydrous ethanol fuel, a significant amount of energy is required for separation and dehydration. Once the azeotrope composition is reached, distillation can no longer be exploited for purification and more expensive methods must be used. Replacing anhydrous ethanol fuel with hydrous ethanol (at the azeotrope composition) can result in significant energy and cost savings during production. The goal of this study was to characterize the volatility behavior and the droplet evaporation dynamics of hydrous and anhydrous ethanol gasoline blends. Three hydrous ethanol-gasoline blends (10, 15, and 30 vol%) in which the hydrous ethanol was composed of the azeotropic proportions of ethanol and water, and three anhydrous ethanol gasoline blends (10, 15, and 30 vol%) were prepared and analyzed with the advanced distillation curve method. Distillation curves were obtained for all test fuels and distillate samples were taken during the distillation process. A droplet evaporation model validated with the distillation data was exploited to understand how the non-ideal volatility behavior of these blends, the high heat of vaporization of water, and altered fluid properties can affect the transient droplet evaporation phenomena and thus the fuel's potential to effectively mix with air in direct injection internal combustion engines. Minor differences in the distillation curves and vapor-liquid equilibrium between the hydrous and anhydrous fuels were measured. Droplet modeling results showed that the higher heat of vaporization and viscosity of water relative to ethanol can lead to significant differences in the net droplet evaporation time between the two types of blends, especially at the higher blending ratios evaluated. These results suggest that the presence of water in ethanol-gasoline blends may extend droplet lifetimes and increase the susceptibility of the fuel to form particulate matter emissions. This is the first study to use distillation methods to gain a better understanding of evaporation behavior and the role of water's non-linear vapor-liquid equilibrium on droplet evaporation dynamics.

Numerical Study of a Direct Injection Internal Combustion Engine Burning a Blend of Hydrogen and Dimethyl Ether

In the reported study, various aspects of dimethyl ether/hydrogen combustion in a Reactivity Controlled Compression Ignition (RCCI) engine are numerically evaluated using Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES). Early direct injection and mixture propagation were also explored, along with peculiaritis of dimethyl ether combustion modeling. The numerical models are validated using available experimental results of a partially premixed dimethyl ether jet flames and an optically accessible internal combustion engine with direct hydrogen injection. LES showed more predictive results in modeling both combustion and mixture propagation. The same models were applied to a full engine cycle of an RCCI engine with stratified reactivity, to gain phenomenological insight into the physical processes involved in stratified reactivity combustion. We showed that 3D and turbulence considerations had a great impact on simulation results, and the LES was able to capture the pressure oscillations typical for this type of combustion.

Direct injection internal combustion engine with high-pressure thermochemical recuperation – Experimental study of the first prototype

The paper describes, for the first time, experimental study results of a novel direct-injection (DI) internal combustion engine (ICE) with high-pressure thermochemical recuperation (HP-TCR) fed by methanol as a primary fuel. The reported system is the first ever working prototype of ICE with HP-TCR. A detailed description of the developed novel technology, physical and chemical processes in the system is presented. HP-TCR system performance is discussed and compared to the previously published study results of the same engine fed with artificially prepared reformate from compressed gas cylinder. HP-TCR demonstrates a significant improvement over the gasoline reference case with 19%–30% relative increase in indicated efficiency and reduction in NOx, CO, HC and CO2 emissions by up to 97, 91, 96 and 15%, respectively. The system performance shows a good prospect to continue the research towards an automotive-scale system development. Further performance improvement options are discussed as well.

Performance and emissions of a direct injection internal combustion engine devised for joint operation with a high-pressure thermochemical recuperation system

This paper presents the results of an experimental study on performance and pollutant emissions of a direct-injection spark-ignition engine devised for joint operation with a high-pressure thermochemical recuperation system based on methanol steam reforming. A comparison with gasoline and ethanol decomposition is performed. Engine feeding with methanol steam reforming products shows an 18%–39% increase in the indicated efficiency and a reduction of 73–94%, 90–96%, 85–97%, and 10–25% in NOx, CO, HC and CO2 emissions, respectively, compared to gasoline within a wide power range. Efficiency improvement and emissions reductions are obtained compared to ethanol decomposition products as well. The possibility of an unthrottled engine operating with a substantially lower cycle-to-cycle variation compared to both gasoline and ethanol decomposition is demonstrated. At high loads, the injector flow area was insufficient for a low injection pressure of 40 bar, leading to late injection and reduced engine efficiency for methanol steam reforming products. In the case of ethanol decomposition, the problem was less severe due to the higher energy content of ethanol decomposition products per mole. The concept of a direct-injection internal combustion engine with high-pressure methanol steam reforming shows good potential, while additional research on injection strategies and gaseous reformate combustion is required.

Models for droplet heating and evaporation: an application to biodiesel, diesel and gasoline fuels

This paper presents our recent progress in the modelling of automotive fuel droplet heating and evaporation processes in conditions close to those in direct-injection internal-combustion engines. Three types of automotive-fuels are considered: biodiesel, diesel and gasoline fuels. Modelling of biodiesel fuel droplets is based on the application of the discrete component (DC) model. A distinctive feature of this model is that it is based on the analytical solutions to the transient heat conduction and species diffusion equations in the liquid phase, taking into account the effects of recirculation. The application of the DC model to fossil fuels (containing potentially hundreds of components), however, is computationally expensive. The modelling of these fuels is based on the recently introduced multi-dimensional quasi-discrete (MDQD) model. This model replaces a large number of components in diesel and gasoline fuels with a much smaller number of quasi-components/components without losing the main features of the original DC model. The MDQD model is shown to accurately predict droplet temperatures and evaporation times and to be much more computationally efficient than the DC model. The main features of these models and their applications to three types of automotive fuel droplets are summarised and discussed.