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For the purpose of achieving carbon-neutrality in the mobility sector by 2050, hydrogen can play a crucial role as an alternative energy carrier, not only for direct usage in fuel cell-powered vehicles, but also for fueling internal combustion engines. This paper focuses on the numerical investigation of high-pressure hydrogen injection and the mixture formation inside a high-tumble engine with a conventional liquid fuel injector for passenger cars. Since the traditional 3D-CFD approach of simulating the inner flow of an injector requires a very high spatial and temporal resolution, the enormous computational effort, especially for full engine simulations, is a big challenge for an effective virtual development of modern engines. An alternative and more pragmatic lagrangian 3D-CFD approach offers opportunities for a significant reduction in computational effort without sacrificing reliability.

The target of the upcoming automotive emission regulations is to promote a fast transition to near-zero emission vehicles. As such, the range of ambient and operating conditions tested in the homologation cycles is broadening. In this context, the proposed work aims to thoroughly investigate the potential of post-oxidation phenomena in reducing the light-off time of a conventional three-way catalyst. The study is carried out on a turbocharged four-cylinder gasoline engine by means of experimental and numerical activities. Post oxidation is achieved through the oxidation of unburned fuel in the exhaust line, exploiting a rich combustion and a secondary air injection dedicated strategy. The CFD methodology consists of two different approaches: the former relies on a full-engine mesh, the latter on a detailed analysis of the chemical reactions occurring in the exhaust line.

Experimental methods and numerical analysis were used to investigate the mechanism of high-speed knocking that occurs in small two-stroke engines. The multi-ion probe method was used in the experiments to visualize flame propagation in the cylinder. The flame was detected by 14 ion probes grounded in the end gas region. A histogram was made of the order in which flames were detected. The characteristics of combustion in the cylinder were clarified by comparing warming up and after warming up and by extracting the features of the cycle in which knocking occurred. As a result, regions of fast flame propagation and regions prone to auto-ignition were identified. In the numerical analysis, flow and residual gas distribution in the cylinder, flame propagation and self-ignition were visualized by 3D CFD using 1D CFD calculation results as boundary conditions and initial conditions.

For the survival of internal combustion engines, the required research right now is for alternative fuels, including drop-ins. Certain types of alternative fuels have been estimated to confirm the superiority in thermal efficiency. In this study, using a single-cylinder engine, olefin and oxygenated fuels were evaluated as a drop-in fuel considering the fuel characteristic parameters. Furthermore, the effect of various additive fuels on combustion speed was expressed using universal characteristics parameters.

This study aimed to achieve both a high compression ratio and low knock intensity in a two-stroke engine. Previous research has suggested that knock intensity can be reduced by combining combustion chamber geometry and scavenging passaging design for the same engine specifications with a compression ratio of 13.7. In this report, we investigate whether low knock intensity can be achieved at compression ratios of 14.4 and 16.8 by adjusting the combustion chamber geometry and scavenging passage design. As a result, the mechanism by which combustion chamber geometry and scavenging passage design change knock intensity was clarified.

In internal combustion engine development, the ongoing research can be mainly classified into two categories based on the purpose: limiting exhaust emissions and searching for alternative fuels. One of the effective approaches reduce emissions is the improvement of thermal efficiency. Certain types of alternative fuels derived from renewable resources were estimated to confirm the thermal efficiency. This study uses a single-cylinder engine added with olefin and oxygenated additive fuel, such as 1-hexene, ethanol, and ETBE, to evaluate the parameters that affect thermal efficiency. Furthermore, the effects of various additive fuels are summarized and essential information is provided for determining next- generation fuel composition.

Lean combustion has been well known to be an effective method to improve the thermal efficiency. However, leaner mixture is prone to cause the unstable combustion and poorer unburned hydrocarbon (UTHC) emissions. Pre-chamber turbulent jet combustion has been proved to enhance the combustion stability under ultra-lean conditions. However, more NOx is formed during the combustion, resulting in the fact that the tailpipe NOx emission is too high to be still not available for the real application. In this report, in order to achieve a higher air excess ratio while keeping lower UTHC emissions, and especially NOx emission, a new combustion technique which combined pre-chamber jet combustion with fuel reforming was proposed and experimentally demonstrated on a pre-chamber engine.

Homogeneous charge compression ignition (HCCI) combustion is promising for not only high thermal efficiency but also reducing nitrogen oxides (NOx) and PM simultaneously. However, the operational range of the HCCI combustion is limited because of some issues, such as poor control of ignition timing and knocking by the excessive rate of pressure rise. In this study, a new combustion system based on the HCCI combustion process is proposed based on the authors' previous experimental work. This combustion system has a divided combustion chamber of two parts, one is small and the other is large. The most significant feature is the small chamber inside the piston. At first, combustion takes place in the small chamber, and then the burned gas is ejected into the large chamber to ignite the mixture in the large chamber.

In order to achieve the climate targets, a mix of different powertrain technologies must be pursued to effectively reduce emissions. By producing hydrogen based on renewable energy sources, it becomes a reasonable choice for fueling internal combustion engines. The specific molecular properties of hydrogen thereby open up new possibilities for favorably influencing the combustion process of engines. The present paper deals with the analysis of a single-cylinder engine with passive pre-chamber ignition and a port fuel injection system, which was adapted for lean hydrogen operation. In this way, the test unit was operated in various load and speed ranges with lambda values from 1.5 to 2.5 and achieved up to 23 bar indicated mean effective pressure. The focus of this work is on the numerical investigation of the hydrogen combustion and its effects on the engine system. Special attention is hereby paid to the influence of different lambda operations.

There is a growing need for low-emissions concepts due to stricter emission regulations, more stringent homologation cycles, and the possibility of a ban on new engines by 2035. Of particular concern are the conditions during a cold start, when the Three-Way Catalyst is not yet heated to its light-off temperature. During this period, the catalyst remains inactive, thereby failing to convert pollutants. Reducing the time needed to reach this temperature is crucial to comply with the more stringent emissions standards. The post oxidation by means of secondary air injection, illustrated in this work, is a possible solution to reduce the time needed to reach the above-mentioned temperature. The strategy consists of injecting air into the exhaust manifold via secondary air injectors to oxidize unburned fuel that comes from a rich combustion within the cylinder.

The race towards zero carbon emissions is ongoing with the need to reduce the consumption of fossil energy resources. This demands immediate and reliable developments regarding technical environmentally friendly solutions for the power and transportation sectors. An alternative way to achieve a carbon-free powertrain is the use of green hydrogen for internal combustion engines. In this work the self-designed Fraunhofer single-cylinder engine with a displacement volume of 430 mm3 developed for extreme lean combustion and passive pre-chamber ignition was adapted for hydrogen engine operation. With hydrogen combustion, the customized cooling system resulting in low metal temperatures is simulated and optimized to avoid hot spots in the combustion chamber. The investigated single-cylinder engine is characterized by a compression ratio of 12.2, port fuel injection and a conventional spark plug.

Following Part 1 of the previous study, this paper reports the structure’s exciting force and summarize the overall research results. An experimental study was conducted to clarify the relationship between engine combustion and vibration, and to establish technology to suppress it. This study focused on the vehicle interior noise caused by combustion in which vibration transmission is the main component at high speed and high load region. A phenomenon in which both the combustion’s exciting force and the structure’s exciting force are combined is defined as vehicle interior noise caused by combustion. Conventionally, combustion and vibration are often discussed in terms of the average cycle, but considering the nonstationary property of vibration, in this paper analyzed the structure’s exciting force characteristics for vibration in cycle-by-cycle. Analysis was conducted using the combustion indicators clarified in the previous study.

This study focused on the vehicle interior noise caused by combustion in which vibration transmission is the main component at high speed and high load region. A phenomenon in which both the combustion’s exciting force and the structure’s exciting force are combined is defined as vehicle interior noise caused by combustion. Conventionally, combustion and vibration are often discussed in terms of the average cycle, but considering the nonstationary property of vibration, in this paper analyzed the combustion characteristics for cycle-by-cycle and investigated indicators for the combustion’s exciting force. The engine vibration is affected by heat release characteristics even with the same engine structure specifications. The heat release characteristics were determined as indicators for the combustion’s exciting force. Transfer Path Analysis (TPA) revealed that there is piston transmission in the target frequency band.

To realize stable combustion in lean or diluted conditions, reducing cycle-to-cycle variations of flow and fuel distribution is important. In this study, the effect of initial flow field was examined by simultaneous Time-Resolved PIV and visualization on two cross-sections in a fully optical-access engine under motoring and firing conditions with homogeneous pre-mixture. As a result, Omega index was defined and plotted on the correlation map between turbulence kinetic energy and CA10 (duration from ignition timing to 10% to the total accumulated heat). The omega index describes the strength of a horizontal flow field that resembles the shape of the Greek letter Omega. The plots with high Omega index were found frequently in the CA10 retarded cycles. On the other hand, the plots with low Omega index have simple tumble flows and the correlation was clearly found.

In order to decarbonize and lower the overall emissions of the transport sector, immediate and cost-effective powertrain solutions are needed. Natural gas offers the advantage of a direct reduction of carbon dioxide (CO2) emissions due to its better Carbon to Hydrogen ratio (C/H) compared to common fossil fuels, e.g. gasoline or diesel. Moreover, an optimized engine design suiting the advantages of natural gas in knock resistance and lean mixtures keeping in mind the challenges of power density, efficiency and cold start manoeuvres. In the public funded project MethMag (Methane lean combustion engine) a gasoline fired three-cylinder-engine is redesigned based on this change of requirements and benchmarked against the previous gasoline engine.

The new CO2 and emissions limits imposed to European manufacturers require the adoption of different innovative solutions, such as the use of potentially CO2-neutral synthetic fuels alongside a tailored development of the internal combustion engine, as an excellent solution to accompany the hybridization of vehicles. Dr.Ing. h.c. F. Porsche AG and FKFS, already partners for the development of engines with eFuels, propose a new study carried out on a research engine, investigating the combination of Porsche synthetic gasoline (POSYN) with an engine with millerization and passive pre-chamber. The use of CO2-neutral fuels allow for an immediate reduction in CO2 emissions from all cars already on the market, particularly since Porsche is one of the manufacturers whose cars remain in use for the longest time. The data collected on a single-cylinder engine test bench, for different fuels, with conventional spark plug are used as input for the calibration of 3D-CFD simulations.

The development of future gasoline engines is dominated by the study of new technologies aimed at reducing the engine negative environmental impact and increase its thermal efficiency. One common trend is to develop smaller engines able to operate in stoichiometric conditions across the whole engine map for better efficiency, lower fuel consumption, and optimal conversion rate of the three-way catalyst (TWC). Water injection is one promising technique, as it significantly reduces the engine knock tendency and avoids fuel enrichment for exhaust temperature mitigation at high power operation. With the focus on reducing the carbon footprint of the automotive sector, another vital topic of research is the investigation of new alternative CO2-neutral fuels or so-called eFuels. Several studies have already shown how these new synthetic fuels can be produced by exploiting renewable energy sources and can significantly reduce engine emissions.

Some SI (spark-ignition) engines fueled with gasoline for industrial machineries are designed based on the conventional diesel engine in consideration of the compatibility with installation. Such diesel engine-based SI engines secure a combustion chamber by a piston bowl instead of a pent-roof combustion chamber widely applied for SI engines for automobiles. In the development of SI engines, because knocking deteriorates the power output and the thermal efficiency, it is essential to clarify causes of knocking and predict knocking events. However, there has been little research on knocking in diesel engine-based SI engines. The purpose of this study is to elucidate knocking phenomena in a gasoline engine with a re-entrant piston bowl and swirl flow numerically and experimentally. In-cylinder visualization and pressure analysis of knock onset cycles have been experimentally performed. Locations of autoignition have been predicted by 3D-CFD analysis with detailed chemical reactions.

In recent years, the improvement in the fuel efficiency and reduction in CO2 emission from internal combustion engines has been an urgent issue. The lean burn technology is one of the key technologies to improve thermal efficiency of SI engines. However, combustion stability deteriorates at lean burn operations. The reduction in cycle-to-cycle and cylinder-to-cylinder variations is one of the major issues to adapt the lean burn technique for production engines. However, the details of the causes and mechanisms for the combustion variations under the lean burn operations have not been cleared yet. The purpose of this study is to control cylinder to cylinder combustion variation. A conventional turbocharged direct injection SI engine was used as the test engine to investigate the effect of engine control parameters on the cylinder to cylinder variations. The engine speed is set at 2200 rpm and the intake pressure is set at 58, 78, 98 kPa respectively.

Knocking occurs within the high-speed range of small two-stroke engines used in handheld work equipment. High-speed knock may be affected by the engine speed and delivery ratio. However, evaluation of these factors independently using experimental methods is difficult. Therefore, in this study, these factors were independently evaluated using numerical calculations. The purpose of this study was to clarify the mechanism by which the intensity of high-speed knocking that occurs in small two-stroke engines becomes stronger. The results suggest that temperature inhomogeneity due to insufficient mixing of fresh air and previously burned gas may induce high-speed knocking in the operating range at high engine speeds.