Experimental Research of Advanced Combustion Modes and Fuels in Internal Combustion Engines

Abstract

This work summarizes the knowledge acquired in several combustion engine research laboratories, within various research projects in the field of advanced combustion in spark ignition engines. The first part will present studies on homogeneous charge compression ignition (HCCI), that has received much attention in recent years due to its ability to reduce both fuel consumption and NO emissions compared to normal spark-ignited (SI) combustion. However, due to the limited operating range of HCCI production feasible engines will need to employ a combination of combustion strategies, such as stoichiometric SI combustion at high loads and leaner burn spark-assisted compression ignition (SACI) and HCCI at intermediate and low loads. The goals of the first two studies were to extend the high load limit of HCCI into the SACI region while maintaining a stoichiometric equivalence ratio. Experiments were conducted on a gasoline-fueled single-cylinder research engine with fully flexible valve actuation. Attention was also given to a comparison of various methods for knock identification and quantification in various combustion modes. The second part presents the experimental and simulation research of an advanced combustion system for a gas engine with indirect ignition using in-house developed actively scavenged prechamber. The concept was adopted from large stationary engines and was designed and optimized to fit the engine for a light duty truck. The work was initiated as an experimental work. However, during the project, it became obvious that a deeper insight into a complex flow and combustion process was needed. Therefore, a CFD simulation has been implemented into the process. In the first stage, the work was focused on the prechamber flow characterization using the CFD without the combustion process. The other two parts then involved a full engine working cycle simulation with a state-of-the-art combustion modeling and LES approach in CFD. Two design variants of the prechamber with different geometries and volume were analyzed. The final part describes an investigation of a low temperature combustion of hydrogen in the internal combustion engine. A hydrogen fueled experimental single cylinder engine was tested in a steady state operation on an engine test bed. The engine was operated in a low-temperature combustion mode with a lean mixture with high air excess ratio _ between 2.6 and 3.0. without any irregular combustion phenomena. A high boost was necessary for achieving sufficient power density at the lean burn mode. The engine reached a high thermal efficiency. Molar fraction of NOx below 10 ppm was achieved within the whole range of operational points. Which means, that the low-temperature combustion showed a potential to comply with contemporary as well as future limits of NOx emission without any exhaust gas aftertreatment. Specific emission of CO2 even involving the CO2 inflow with intake air was lowered by 2 to 3 orders of magnitude compared to state-of-the-art automotive diesel engines. Emission of other gaseous pollutants as well as emission of particulate matter were negligible.