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In the present paper the results of a set of experimental investigations on LSPI are discussed. The ignition system of a test engine was modified to enable random spark advance in one of the four cylinders. LSPI sequences were successfully triggered and exhibited similar characteristics compared to regularly occurring pre-ignition. Optical investigations applying a high speed camera system enabling a visualization of the combustion process were performed. In a second engine the influence of the physical properties of the considered lubricant on the LSPI frequency was analyzed. In addition different piston ring assemblies have been tested. Moreover an online acquisition of the unburned hydrocarbon emissions in the exhaust gas was performed. The combination of these experimental techniques in the present study provided further insights on the development of LSPI sequences.

Small gasoline engines are used in motorcycles and handheld machinery, because of their high power density, low cost and compact design. The reduction of hydrocarbon emissions and fuel consumption is an important factor regarding the upcoming emission standards and operational expenses. The scavenging process of the two-stroke engine causes scavenging losses. A reduction in hydrocarbon emissions due to scavenging losses can be achieved through inner mixture formation using direct injection (DI). The time frame for fuel vaporization is limited using two-stroke SI engines by the high number of revolutions. A high pressure DI system was used to offer fast and accurate injections. An injection pressure of up to 140 MPa was provided by a common rail system, built out of components normally used in automotive engineering. A standard electromagnetic injector is applied for the fuel injection. This injection unit is dimensioned for multi-point injections in diesel engines.

Particle number measurements during different real world and legislative driving cycles show that catalyst heating, cold and transient engine operation cause increased particle number emissions. In this context the quality of mixture formation as a result of injector characteristics, in-cylinder flow, operation & engine parameters and fuel composition is a major factor. The goal of this paper is to evaluate the influence of different biogenic and alkylate fuels on the gaseous and particle number emission behavior during catalyst heating operation on a single-cylinder DISI engine. The engine is operated with a late ignition timing causing a high exhaust enthalpy flow to heat up the catalyst, a slightly lean global air fuel ratio to avoid high hydrocarbon emissions and a late injection right before the ignition to reduce the coefficient of variance of the indicated mean effective pressure.

High frequency ignition (HFI) and conventional transistor coil ignition (TCI) were investigated with an optically accessible single-cylinder research engine to gain fundamental understanding of the chemical reactions taking place prior to the onset of combustion. Instead of generating heat in the gap of a conventional spark plug, a high frequency / high voltage electric field is employed in HFI to form chemical radicals. It is generated using a resonant circuit and sharp metallic tips placed in the combustion chamber. The setup is optimized to cause a so-called corona discharge in which highly energized channels (streamers) are created while avoiding a spark discharge. At a certain energy the number of ionized hydrocarbon molecules becomes sufficient to initiate self-sustained combustion. HFI enables engine operation with highly diluted (by air or EGR) gasoline-air mixtures or at high boost levels due to the lower voltage required.

The combustion processes optimization is one of the most important factors to enhancing thermal efficiency and reducing exhaust emissions of combustion engines [1; 2]. Future emission regulations for small two-stroke SI engines require that the emissions of gases causing the greenhouse effect, such as carbon dioxide, to be reduced. One possible way to reduce exhaust gas emissions from two-stroke small off-road engines (SORE) is to use biogenic fuels. Because of their nearly closed carbon dioxide circuit, the emissions of carbon dioxide decrease compared to the use of fossil fuels. Also biogenic fuels have a significant influence on the combustion process and thus the emissions of different exhaust gas components may be reduced. Besides greenhouse gases, several other exhaust gas components need to be reduced because of their toxicity to the human health. For example, aromatic hydrocarbons cause dangerous health problems, and can be reduced by using alkylate fuel.

Rapeseed oil can be a possible substitute for fossil fuel in Diesel engines. Due to different physical properties of rapeseed oil like higher viscosity and higher compressibility compared to diesel fuel, rapeseed oil cannot be easily used in conventional Diesel engines without modifications. Especially incomplete combustion leads to deposits in the combustion chamber and higher exhaust gas emissions. These unfavorable characteristics are caused primarily by insufficient mixture preparation. The adjustment of the injection system will improve the mixture preparation and the combustion of a Diesel engine, operated with rapeseed oil. The nozzle geometry is the main parameter of the whole injection system chain to realize a better combustion process and so higher efficiency and lower exhaust gas emissions.

The quality of mixture formation and the combustion process is of significant importance for reducing the hydrocarbon emissions of small two stroke engines. The scope of this work was to investigate the mixture conditions after the exhaust closes and after the end of combustion depending on various engine operating points. For this experimental investigation a Gas Sampling Valve (GSV) was combined with a flame ionisation detector (FID) and a CO2-analyser. Using this technique, it was possible to measure the hydrocarbon concentration after end of combustion. Furthermore the local residual gas concentration after exhaust closes was determined. To allow for a comparison of the experimental results with calculations with CFD codes, in cylinder pressure measurement and exhaust gas measurements are done additionally.

The focus of this work was to determine the influence of spray targeting on temperature distributions, combustion progress and unburned hydrocarbon (HC) emissions at cold operating conditions, and to show the capability of model and full engine tests adapted for different measurement techniques. A comprehensive study applying endoscopic visualization, infrared thermography, combustion and emission measurements was carried out in a 4-stroke 4-cylinder 16-valve production engine with intake port injection during different engine operating conditions including injection angle and timing. In addition 2D visualization and PIV measurements were performed in a back-to-back model test section with good optical access to the intake manifold and the combustion chamber. The measurements in both set ups were in good agreement and show that model tests could lead to useful findings for a real engine.