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Lean burn combustion concepts with high mean effective pressures are being pursued for large gas engines in order to meet future stringent emission limits while maintaining high engine efficiencies. Since severe boundary conditions for the ignition process are encountered with these combustion concepts, the processes of spark ignition and flame initiation are important topics of applied research, which aims to avoid misfiring and to keep cycle-to-cycle combustion variability within reasonable limits. This paper focuses on the fundamental investigation of early flame kernel development using different ignition system settings. The investigations are carried out on a rapid compression-expansion machine in which the spark ignition process can be observed under engine-like pressure and excess air ratio conditions while low flow velocities are maintained.

Using natural gas in large bore engines reduces carbon dioxide emissions by up to 25% at a lower fuel cost than diesel engines. In demanding applications with highly transient operating profiles, however, premix gas engines have disadvantages compared to diesel engines because of the potential for knocking and misfire to occur. Operating a gas engine using the diesel cycle requires high gas injection pressures. Furthermore, a source of ignition is needed due to the high autoignition temperature of methane. State-of-the-art solutions inject a small quantity of diesel fuel before introducing the natural gas. One monofuel alternative ignites the gas jets with flame torches that originate in a prechamber. This paper presents the simulation based development of a prechamber ignited high pressure direct injection (HPDI) gas combustion concept and subsequent experimental validation.

Optimization of engine warm-up behavior has traditionally made use of experimental investigations. However, thermal engine models are a more cost-effective alternative and allow evaluation of the fuel saving potential of thermal management measures in different driving cycles. To simulate the thermal behavior of engines in general and engine warm-up in particular, knowledge of heat distribution throughout all engine components is essential. To this end, gas-side heat transfer inside the combustion chamber and in the exhaust port must be modeled as accurately as possible. Up to now, map-based models have been used to simulate heat transfer and fuel consumption; these two values are calculated as a function of engine speed and load. To extend the scope of these models, it is increasingly desirable to calculate gas-side heat transfer and fuel consumption as a function of engine operating parameters in order to evaluate different ECU databases.

A realistic modeling of the wall heat transfer is essential for an accurate analysis and simulation of the working cycle of internal combustion engines. Empirical heat transfer formulations still dominate the application in engine process simulations because of their simplicity. However, experiments have shown that existing correlations do not provide satisfactory results for all the possible operation modes of hydrogen internal combustion engines. This paper describes the application of a flow field-based heat transfer model according to Schubert et al. [1]. The models strength is a more realistic description of the required characteristic velocity; considering the influence of the injection on the global turbulence and on the in-cylinder flow field results in a better prediction of the wall heat transfer during the compression stroke and for operations with multiple injections. Further an empirical hypothesis on the turbulence generation during combustion is presented.

A realistic simulation of the wall heat transfer is an imperative condition for the accurate analysis and simulation of the working process of IC engines. Due to its simplicity in application, zero-dimensional wall heat transfer models dominate engine cycle simulation in practice. However, experience shows that existing zero-dimensional models for wall heat transfer do not yield satisfactory results in certain applications. This is mainly due to a lack of consideration of the actual flow field in the cylinder. In this paper a quasi-dimensional heat transfer model, which is based on a detailed description of the turbulent flow field in the combustion chamber, is described. The model presents a consistent approach for the high pressure as well as the low pressure part of the cycle. The results of the heat transfer model are compared with results from the correlation by Woschni/Huber and with experimental results from various DI Diesel engines.

Hydrogen is frequently cited as a future energy carrier. Hydrogen allows a further optimization of internal combustion engines, especially with direct injection. In order to assess various concepts, detailed thermodynamic analyses were carried out. Effects, which can be neglected with conventional fuels (e.g. losses due to injection during compression stroke) are considered. These basics as well as several results from test bed investigations are described within this article. Wall heat losses were found to have a major influence on overall efficiency and are thus investigated in detail, based on local surface temperature measurement. Finally, concepts that allow an increase in engine efficiency and lowest NOx emissions are demonstrated.

The 3D CFD method has become an essential and reliable tool for the development of modern large gaseous-fuelled engines. This holds especially true for the optimization of mixture formation and charge motion in prechamber engines to ensure suitable conditions near the spark plug at ignition time. In order to initialize a quick combustion process, an ignitable mixture with high turbulence but moderate velocity must prevail round the spark plug. However, suitable models for combustion and heat transfer are inevitable for a realistic simulation of the whole engine cycle. Within 3D CFD codes the combustion process is usually calculated using the PDF (probability density function) - model; heat transfer is modeled based on the logarithmic wall function. Experimental investigations were carried out on a single cylinder research engine in order to validate the combustion model used and different heat transfer models.

This paper summarizes the results of several investigations on in-cylinder heat transfer during high-pressure and gas exchange phases as well as heat transfer in the inlet and outlet ports for a number of different engine types (DI Diesel, SI and gaseous fueled engine). The paper contains a comparision of simulation results and experimental data derived from heat flux measurements. Numerical results were obtained from zero-, one- and three-dimensional simulation methods. Time and spatially resolved heat fluxes were measured applying the surface temperature method and special heat flux sensors. The paper also includes an assessment of different sensor types with respect to accuracy and applicability.