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Heavy-duty vehicles are primarily powered by diesel fuel, emitting CO2 emissions regardless of the exhaust after-treatment system. Contrastingly, a hydrogen engine has the potential to decarbonize the transportation sector as hydrogen is a carbon free, renewable fuel. In this study, a multi-physics 1D simulation tool (GT-Power) is used to model the gas exchange process and performance prediction of a two-stroke hydrogen engine. The aim is to establish a maximum torque-level for a four-stroke hydrogen engine and then utilize different methods for two-stroke modeling to achieve similar torque by optimizing the gas exchange process. A camless engine is used as base, enabling the flexibility to utilize approximately square valve lift profiles. The preliminary step is the GT-Power model validation, which has been done using diesel and hydrogen engines (single-cylinder heavy-duty) experiments at different operating points (871 rpm, 1200 rpm, 1259 rpm, and 1508 rpm).

This paper investigates how particulates number PN is influenced by fuel wall-film, liner wetting, and the mixing quality for different start of injection timings (SOI). Both experimental data with PN measurements, endoscope images from a high-speed camera from a single-cylinder engine, and CFD simulations were used for the analysis. Engine geometry was a spray-guided system with 300 bar fuel pressure and with single injections. Data was captured for 2000 rpm / 9 bar IMEPn. The results show that fuel film on the piston was only found to significantly increase PN for over-advanced SOI (in our engine geometry, earlier than -310 CAD). This results in luminescence from diffusion burn on the piston surface, which strongly contributes to PN. For an SOI timing of -310 CAD, fuel film on piston reaches a maximum of 3% of the injected fuel, vaporizes, and no remaining fuel film is found at the time of ignition. Approximately 0.5-1% of the fuel ends up on the liner.

Pre-chamber combustion (PCC) has re-emerged in recent last years as a potential solution to help to decarbonize the transport sector with its improved engine efficiency as well as providing lower emissions. Research into the combustion process inside the pre-chamber is still a challenge due to the high pressure and temperatures, the geometrical restrictions, and the short combustion durations. Some fundamental studies in constant volume combustion chambers (CVCC) at low and medium working pressures have shown the complexity of the process and the influence of high pressures on the turbulence levels. In this study, the pre-chamber combustion process was investigated by combustion visualization in an optically-accessible pre-chamber under engine relevant conditions and linked with the jet emergence inside the main chamber. The pre-chamber geometry has a narrow-throat. The total nozzle area is distributed in two six-hole rows of nozzle holes.

Gasoline direct injection (GDI) engines usually emit higher levels of particulates in warm-up conditions of a driving cycle. Thus, sources of soot formation in these conditions were investigated by measuring particulate numbers (PN) emitted from a single-cylinder GDI engine and their sizes. The combustion was also visualized using an endoscope connected to a high-speed camera. Engine coolant and oil temperatures were varied between 15 and 90oC to mimic warm-up conditions. In addition, effects of delaying the start of ignition (SOI) on the emissions in these conditions were examined. Coolant and oil temperatures were varied individually to identify which factor has most effect on PN emissions. While coolant temperature strongly influenced PN with cold oil, the oil temperature insignificantly affected PN at low coolant temperature. These findings indicate that PN emissions are heavily dependent on the engine block’s temperature, which is dominated by the coolant.

The potential of 48V Mild Hybrid is promising in meeting the present and future CO2 legislations. There are various system layouts for 48V hybrid system including P0, P1, P2. In this paper, P2 architecture is used to investigate the effects of water injection benefits in a mild hybrid system. Electrification of the conventional powertrain uses the benefits of an electric drive in the low load-low speed region where the conventional SI engine is least efficient and as the load demand increases the IC Engine is used in its more efficient operating region. Engine downsizing and forced induction trend is popular in the hybrid system architecture. However, the engine efficiency is limited by combustion knocking at higher loads thus ignition retard is used to avoid knocking and fuel enrichment becomes must to operate the engine at MBT (Maximum Brake Torque) timing; in turn neutralizing the benefits of fuel savings by electrification.

Homogeneous lean combustion (HLC) can be utilized to substantially improve spark ignited (SI) internal combustion engine efficiency. Higher efficiency is vital to enable clean, efficient and affordable propulsion for the next generation light duty vehicles. More research is needed to ensure robustness, fuel efficiency/NOx trade-off and utilization of HLC. Utilization can be improved by expanding the HLC operating window to higher engine torque domains which increases impact on real driving. The authors have earlier assessed boosted HLC operation in a downsized two-litre engine, but it was found that HLC operation could not be achieved above 15 bar NMEP due to instability and knocking combustion. The observation led to the conclusion that there exists a lean load limit. Therefore, further experiments have been conducted in a single cylinder research DISI engine to increase understanding of high load lean operation.

To act on global warming, CO2 emissions must be reduced. This will require a reduction in the use of fossil fuels for transportation. Because of the large quantities of fossil fuels used in transportation, sources of renewable fuels other than biomass will have to be explored, such as electrofuels synthesized from CO2 using renewable electricity. Potential electrofuels include methanol and ethanol, which have shown promising results in SI engines. However, their low cetane numbers make these fuels unsuitable for CI engines because of their poor auto-ignition qualities. The main objective of this study was to evaluate the viability of using methanol and ethanol in CI engines at compression ratios of 16.7 and 20 with a pilot-main injection strategy in the PPC/CI regime. Single cylinder engine tests on a heavy duty engine were performed under medium load conditions (1262 rpm and 172 Nm).

48V mild hybrid powertrains are promising technologies for cost-effective compliance with future CO2 emissions standards. Current 48V powertrains with integrated belt starter generators (P0) with downsized engines achieve CO2 emissions of 95 g/km in the NEDC. However, to reach 75 g/km, it may be necessary to combine new 48V powertrain architectures with alternative fuels. Therefore, this paper compares CO2 emissions from different 48V powertrain architectures (P0, P1, P2, P3) with different electric power levels under various driving cycles (NEDC, WLTC, and RTS95). A numerical model of a compact class passenger car with a 48V powertrain was created and experimental fuel consumption maps for engines running on different fuels (gasoline, Diesel, E85, CNG) were used to simulate its CO2 emissions. The simulation results were analysed to determine why specific powertrain combinations were more efficient under certain driving conditions.

The effects of using n-butanol, n-octanol, fossil Diesel, hydrotreated vegetable oil (HVO), and blends of these fuels on spray penetration, flame and soot characteristics were investigated in a high-pressure high-temperature constant volume combustion chamber designed to mimic a heavy duty Diesel engine. Backlight illumination was used to capture liquid and vapor phase spray images with a high-speed camera. The flame lift-off length (LOL) and ignition delay were determined by analyzing OH* chemiluminescence images. Laser extinction diagnostics were used to measure the spatially and temporally resolved soot volume fraction. The spray experiments were performed by injecting fuels under non-combusting (623 K) and combusting (823 K) conditions at a fixed ambient air density of 26 kg/m3. A Scania 0.19 mm single straight hole injector and Scania XPI common rail fuel supply system were used to produce injection pressures of 120 MPa and 180 MPa.

Increasing the injection pressure in gasoline direct injection engines has a substantial potential to reduce emissions while maintaining a high efficiency in spark ignition engines. Present gasoline injectors are operating in the range of 20 MPa to 25 MPa. Now there is an interest in higher fuel injection pressures, for instance, around 40 MPa, 60 MPa and even higher pressures, because of its potential for further emission reduction and fuel efficiency improvements. In order to fully utilize the high-pressure fuel injection technology, a fundamental understanding of gasoline spray characteristics is vital to gain insight into spray behavior under such high injection pressures. The understanding achieved may also be beneficial to improve further model development and facilitate the integration of such advanced injection systems into future gasoline engines.

Natural gas, biogas, and biomethane are attractive fuels for compressed natural gas (CNG) engines because of their beneficial physical and chemical characteristics. This paper examines three combustion modes - homogeneous stoichiometric, homogeneous lean burn, and stratified combustion - in an optical single cylinder engine with a gas direct injection system operating with an injection pressure of 18 bar. The combustion process in each mode was characterized by indicated parameters, recording combustion images, and analysing combustion chemiluminescence emission spectra. Pure methane, which is the main component of CNG (up to 98%) or biomethane (> 98 %), was used as the fuel. Chemiluminescence emission spectrum analysis showed that OH* and CN* peaks appeared at their characteristic wavelengths in all three combustion modes. The peak of OH* and broadband CO2* intensities were strongly dependent on the air/fuel ratio conditions in the cylinder.

Look ahead information can be used to improve the powertrain’s fuel consumption while efficiently controlling exhaust emissions. A passenger car propelled by a Euro 6d capable diesel engine is studied. In the conventional approach, the diesel powertrain subsystem control is rule based. It uses no information of future load requests but is operated with the objective of low engine out exhaust emission species until the Exhaust After-Treatment System (EATS) light off has occurred, even if fuel economy is compromised greatly. Upon EATS light off, the engine is operated more fuel efficiently since the EATS system is able to treat emissions effectively. This paper presents a supervisory control structure with the intended purpose to operate the complete powertrain using a minimum of fuel while improving the robustness of exhaust emissions.

The compression ratio is an important engine design parameter. It determines to a large extend engine properties like the achievable efficiency, the heat losses from the combustion chamber and the exhaust losses. The same properties are affected by insulation of the combustion chamber. It is therefore especially important to know the compression ratio when doing experiments with thermal barrier coatings (TBC). In case of porous TBCs, the standard methods to measure the compression ratio can give wrong results. When measuring the compression ratio by volume, using a liquid, it is uncertain if the liquid fills the total porous volume of the coating. And for a thermodynamic compression ratio estimation, a model for the heat losses is needed, which is not available when doing experiments with insulation. The subject of this paper is the evaluation of an alternative method to assess the compression ratio.

Due to stricter emission regulations and more environmental awareness, the powertrain systems are moving toward higher fuel efficiency and lower emissions. In response to these pressing needs, new technologies have been designed and implemented by manufacturers. As a result of increasing complexity of the powertrain systems, their control and optimization become more and more challenging. Virtual powertrain calibration, also known as model-based calibration, has been introduced to transfer a part of test bench testing into a virtual environment, and hence considerably reduce time and cost of product development process while increasing the product quality. Nevertheless, virtual calibration has not yet reached its full potential in industrial applications. Volvo Penta has recently developed a virtual test cell named VIRTEC, which is used in an ongoing pilot project to meet the Stage V emission standards.

Stratified combustion in gasoline engines constitutes a promising means of achieving higher thermal efficiency for low to medium engine loads than that achieved with combustion under standard homogeneous conditions. However, creating a charge that leads to a stable efficient low-emission stratified combustion process remains challenging. Combustion through a stratified charge depends strongly on the dynamics of the turbulent fuel-air mixing process and the flame propagation. Predictive simulation tools are required to elucidate this complex mixing and combustion process under stratified conditions. For the simulation of mixing processes, combustion models based on large-eddy turbulence modeling have typically outperformed the standard Reynolds averaged Navier-Stokes methods.

Laws concerning emissions from heavy duty (HD) internal combustion engines are becoming increasingly stringent. New engine technologies are needed to satisfy these new requirements and to reduce fossil fuel dependency. One way to achieve both objectives can be to partially replace fossil fuels with alternatives that are sustainable with respect to emissions of greenhouse gases, particulates and nitrogen oxides (NOx). A suitable candidate is methanol. The aim of the study presented here was to investigate the possible advantages of combusting methanol in a heavy duty Diesel engine. Those are, among others, lower particulate emissions and thereby bypassing the NOx-soot trade-off. Because of methanol’s poor auto-ignition properties, Diesel was used as an igniting sources and both fuels were separately direct injected. Therefore, two separate standard common rail Diesel injection systems were used together with a newly designed cylinder head and adapted injection nozzles.

Many new combustion concepts are currently being investigated to further improve engines in terms of both efficiency and emissions. Examples include homogeneous charge compression ignition (HCCI), lean stratified premixed combustion, stratified charge compression ignition (SCCI), and high levels of exhaust gas recirculation (EGR) in diesel engines, known as low temperature combustion (LTC). All of these combustion concepts have in common that the temperatures are lower than in traditional spark ignition or diesel engines. To further improve and develop combustion concepts for clean and highly efficient engines, it is necessary to develop new computational tools that can be used to describe and optimize processes in nonstandard conditions, such as low temperature combustion.

Today numerical models are a major part of the diesel engine development. They are applied during several stages of the development process to perform extensive parameter studies and to investigate flow and combustion phenomena in detail. The models are divided by complexity and computational costs since one has to decide what the best choice for the task is. 0D models are suitable for problems with large parameter spaces and multiple operating points, e.g. engine map simulation and parameter sweeps. Therefore, it is necessary to incorporate physical models to improve the predictive capability of these models. This work focuses on turbulence and mixing modeling within a 0D direct injection stochastic reactor model. The model is based on a probability density function approach and incorporates submodels for direct fuel injection, vaporization, heat transfer, turbulent mixing and detailed chemistry.

Many technological developments in automobile powertrains have been implemented in order to increase efficiency and comply with emission regulations. Although most of these technologies show promising results in official fuel economy tests, their benefits in real driving conditions and real driving emissions can vary significantly, since driving profiles of many drivers are different than the official driving cycles. Therefore, it is important to assess these technologies under different driving conditions and this paper aims to offer an overall perspective, with a numerical study in simulations. The simulations are carried out on a compact passenger car model with eight powertrain configurations including: a naturally aspirated spark ignition engine, a start-stop system, a downsized engine with a turbocharger, a Miller cycle engine, cylinder deactivation, turbocharged downsized Miller engine, a parallel hybrid electric vehicle powertrain and an electric vehicle powertrain.

The current trend toward more fuel efficient vehicles with lower emission levels has prompted development of new combustion techniques for use in gasoline engines. Stratified combustion has been shown to be a promising approach for increasing the fuel efficiency. However, this technique is hampered by drawbacks such as increased particulate and standard emissions. This study attempts to address the issues of increased emission levels by investigating the influence of high frequency ionizing ignition systems, 350 bar fuel injection pressure and various tumble levels on particulate emissions and combustion characteristics in an optical SGDI engine operated in stratified mode on isooctane. Tests were performed at one engine load of 2.63 bar BMEP and speed of 1200 rpm. Combustion was recorded with two high speed color cameras from bottom and side views using optical filters for OH and soot luminescence.