Ulrich Spicher

Knock Behavior of SI-Engines: Thermodynamic Analysis of Knock Onset Locations and Knock Intensities

A general definition and an index for the assessment of different engine knock behavior have been developed. The knock onset locations have been determined by piezoresistive pressure actuators and optical fiber probes in full load engine operation mode. The thermodynamic conditions at the knock onset locations have been quantified by CFD-calculations. Therefore the local fuel concentration, mixture temperature and residual gas concentration have been considered. These calculated thermodynamic conditions were further used to calculate the necessary volume of an exothermal center for the generation of the maximal measured pressure amplitudes.

Measurements of spatial flame propagation and flow velocities in a spark ignition engine

Knowledge of flame propagation and flow characteristics enables a more detailed description of in-cylinder processes as well as assessing the influences of engine operating conditions and design parameters, particularly in regard to fuel economy and emission control. Spatial flame propagation in a single-cylinder spark-ignition engine is studied by a measuring technique that uses optical fibers coupled with photomultipliers. The propagation process is monitored through a large number of optical fibers arranged in a matrix in the combustion chamber wall. The spatial flame front shape, the flame volume, and the flame front velocity as a function of time are derived from these measurements. A dual beam laser-doppler-velocimeter (LDV), operating in forward scatter mode, is used to measure flow velocities of fluid motion in a motored and fired engine. Measurements are performed at several points within the combustion chamber. Signal processing is done by a counter. By averaging measurements over several engine cycles, mean flow velocity and RMS values are obtained. It was found that increasing the air-fuel ratio decreases the flame propagation rate and the burning velocity, whereas mean flow velocities of fluid motion are hardly affected. Swirl flow, generated by a shrouded inlet valve, leads to higher mean flow velocities, higher flame front velocities, and higher burning velocities, and the flame front is deformed.

Influence of Operating Parameters on the Thermal Behavior and Energy Balance of an Automotive Diesel Engine

The paper gives a comprehensive overview regarding all relevant operation parameters mainly influencing the energy balance of a state-of-the-art automotive Diesel engine. A detailed experimental analysis of the influence of injection timing and pressure, EGR rate, boost pressure, charge air temperature, coolant temperature and swirl flap position is presented. The investigation includes combustion chamber energy balances based on pressure trace analyses (internal energy balance) as well as outer energy balances that take into account all outgoing and incoming energy flows of the engine based on extensive temperature and flow measurements of the relevant fluids. Measurements of the engine structure temperatures are used to complete the analysis of the thermal engine behaviour depending on the operating parameters. The aim of the paper is to give an overview which operating parameters are crucial for thermal engine application and simulation.

Experimentelle Untersuchungen zur Entwicklung des kurbelwinkelaufgelösten Brennraumluftverhältnisses im Transientbetrieb eines Ottomotors mit Direkteinspritzung

Mit der absehbaren Einfuhrung neuer gesetzlicher Zertifizierungszyklen (WLTP) und unter Berucksichtigung des realen Kundenfahrverhaltens (RDE – Real Driving Emissions), gewinnt die Untersuchung der transienten Betriebsphasen eines Verbrennungsmotors zunehmend an Bedeutung. Eine detaillierte Analyse dieser Ubergangszustande stellt dabei besondere Herausforderungen sowohl an die eingesetzte Messtechnik als auch an die angewandte Entwicklungsmethodik. Dies wird vor dem Hintergrund deutlich, dass meist nur einige wenige Arbeitsspiele wahrend dieser transienten Betriebsphasen fur die vergleichsweise hohen Emissionen verantwortlich sind.