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The reduction of anthropogenic greenhouse gas emissions and ever stricter regulations on pollutant emissions in the transport sector require research and development of new, climate-friendly propulsion concepts. The use of renewable hydrogen as a fuel for internal combustion engines promises to provide a good solution especially for commercial vehicles. For optimum efficiency of the combustion process, hydrogen-specific engine components are required, which need to be tested on the test bench and analysed in simulation studies. This paper deals with the simulation-based investigation and optimisation of fuel injection in a 6-cylinder PFI commercial vehicle engine, which has been modified for hydrogen operation starting from a natural gas engine concept.

Dual-fuel engines powered by renewable fuels provide a potential solution for reducing the carbon footprint and emissions of transportation, contributing to the goal of achieving sustainable mobility. The investigation presented in the following uses a dual-fuel engine concept running on biogas (referred to as CNG in this paper) and the e-fuel polyoxymethylene dimethyl ether (OME). The current study focuses on the effects of exhaust gas rebreathing and external exhaust gas recirculation (EGR) on emissions and brake thermal efficiency (BTE). A four-cylinder heavy-duty engine converted to dual-fuel operation was used to conduct the engine tests at a load point of 1600 min-1 and 9.8 bar brake mean effective pressure (BMEP). The respective shares of high reactivity fuel (HRF, here: OME) and low reactivity fuel (LRF, here: CNG) were varied, as were the external and internal EGR rates and their combinations.

With the rising popularity of dual-fuel combustion, liquefied petroleum gas (LPG) can be utilized in high-compression diesel engines. Through production from biomass (biomass to liquid, BtL), biopropane as a direct substitute for LPG can contribute to a reduction in greenhouse gas emissions caused by combustion engines. In a conventional dual-fuel engine, the low reactivity fuel (LRF) propane is premixed with the intake air to form a homogeneous mixture. This air-fuel mixture is then ignited by the high reactivity fuel (HRF) in the form of a diesel pilot injection inside the cylinder. In the presented work, this premixed charge operation (PCO) is compared to a method where propane and diesel are blended directly upstream of the high-pressure pump (premixed fuel operation, PFO) in variable mixing ratios for different engine loads and speeds. Furthermore, the effects of internal and external exhaust gas recirculation are investigated for each operating mode.

In recent years, the automotive industry has shifted from purely combustion engine-driven vehicles towards hybridization due to the introduction of CO2 emission legislation. Hybrid powertrains also represent an important pillar and starting point in the journey towards zero-emission and full electrification. Fulfilling the most recent emission standards requires efficient control strategies for the engine, capable of real-time operation. Model accuracy is one of the main parameters which directly influence the performance of such control strategies. Specific methodologies developed in the past, such as physically- or phenomenologically-based approaches, have already facilitated the modeling of the combustion engine. Even though these models can accurately predict emissions in steady state conditions, their performance during transient engine operation is time-consuming and still not sufficiently reliable.

The move away from fossil fuels and the diversification of the primary energy sources used are imperative both in terms of mitigating global warming and ensuring the political independence of the Western world. For the industries of agriculture and forestry, it is possible to secure the basic energy supply through their own yield. The use of vegetable oil is a possibility to satisfy the energy requirements for agricultural machines both autonomously and sustainably. Up to now, rapeseed has been the most important plant for oil production in Western Europe. In the EU, rapeseed oil is currently credited with up to 60% fossil CO2 savings compared to conventional diesel fuel. As a result, since 2018, rapeseed oil is no longer considered as biofuel in the EU. However, if cultivation and processing are completely based on renewable energy sources, up to 90% of fossil CO2 emissions can be saved in the future. This also applies to rapeseed oil, which is a by-product of animal feed production.

In recent years, the utilization of dual-fuel combustion has gained popularity in order to improve engine efficiency and emissions. With its high knock resistance, methane allows operation in high compression diesel engines with lower risk of knocking. With the use of diesel fuel as an ignition source, it is possible to exploit the advantages of lean combustion without facing problems to provide the high amount of ignition energy necessary to burn methane under such operating conditions. Another advantage is the variety of sources from which the primary fuel can be obtained. In addition to fossil sources, methane can also be produced from biomass or electrical energy. As the rate of substitution of diesel by methane increases, the trade-off between nitrogen oxide and soot is mitigated. However, emissions of carbon monoxide and unburned methane increase.

The aim of current research on internal combustion engines is to further reduce exhaust gas pollutant emissions while simultaneously lowering carbon dioxide emissions in order to limit the greenhouse effect. Due to the restricted potential for reducing CO2 (carbon dioxide) emissions when using fossil fuels, an extensive defossilisation of the transport sector is necessary. Investigations of future propulsion systems should therefore not focus solely on further development of the prime mover, but also on the energy carrier which is used. In this context, fuels from renewable energy sources are of particular interest, e.g. paraffinic diesel fuels such as hydrogenated vegetable oil (HVO) or potentially entirely synthetic fuels like POMDME (polyoxymethylene dimethyl ether, short: OME) as well as blends of such fuels.

The use of vegetable oil as a fuel for agricultural and forestry vehicles allows a CO2 reduction of up to 60 %. On the other hand, the availability of vegetable oil is limited, and price competitiveness depends heavily on the respective oil price. In order to reduce the dependence on the availability of specific fuels, the joint research project “MuSt5-Trak” (Multi-Fuel EU Stage 5 Tractor) aims at developing a prototype tractor capable of running on arbitrary mixtures of diesel and rapeseed oil. Depending on the fuel mixture used, the engine parameters need to be adapted to the respective operating conditions. For this purpose, it is necessary to detect the composition of the fuel mixture and the fuel quality. Regardless of the available fuel mixture, all functions for regular engine operation must be maintained.

New engine concepts such as Miller, HCCI or highly diluted combustion offer great potential for further optimization of ICEs in terms of fuel economy and pollutant emissions. However, the development of such concepts requires a high degree of variability in the control of gas exchange, characterized by variability in valve spread, maximum valve lift and - ideally independent of these two variables - in valve opening time. In current series variable valvetrains, valve lift and opening duration are usually directly dependent one from the other. In the ideal case, however, engine concepts such as Miller require a fully flexible variation of the closing time of the intake valve while still maintaining the same intake opening time. Here, a methodology for the geometric layout of fully variable valve trains with significantly extended functionalities is presented. In this concept, the control of the valve opening and closing events is distributed to two synchronously rotating cam disks.

For the optimization and extension of operating range of future combustion systems aiming at ultra-low emissions and high efficiency, the control of gas exchange plays a major role. Important parameters for optimization are e.g. volumetric efficiency, residual gas control, in-cylinder charge motion and precise control of the level of homogeneity or inhomogeneity of the charge as required by the particular combustion mode. In addition, advanced operating modes such as Miller or Atkinson cycle or gasoline compression ignition demand a high degree of variability in cam timing. A highly flexible variable valvetrain has been designed for the investigation and development of such new combustion processes. This novel valvetrain is based on a mechanically fully variable actuation concept using two independently rotating cam disks per valve. By this arrangement, new degrees of freedom in the design of the valve opening curve arise.

Today, downsizing through active displacement control is in series production using cylinder deactivation (CDA) concepts. However, current systems deactivating two cylinders of a four-cylinder engine are limited regarding the effective CO2 saving potential due to the confined usable operating range of the two-cylinder mode. Therefore, the objective of the current investigation is a three-cylinder engine with the possibility to activate an additional (fourth) cylinder. For this purpose, a four-cylinder series engine was modified to the firing order of a three-cylinder engine for the first three cylinders. The exterior cylinders 1 and 4 are operated in parallel, with the fourth cylinder deactivated in efficiency mode. Launching and idle mode are also operated with three active cylinders. Additional modifications to the valve train were carried out in order to further exploit the increased residual gas tolerance due to the load point shift.

Homogeneous Charge Compression Ignition (HCCI) offers a significant potential to reduce CO2 as well as NOx and particulate emissions. However ensuring stable and efficient HCCI combustion in practical use is a challenge and requires sophisticated control concepts. In the present paper a closed loop control concept is investigated for this purpose. In order to optimize the closed loop control, adaptations with neural networks are introduced. Different sensor concepts for HCCI combustion control are presented and the benefit of the analysis of crankshaft movements is analyzed.