Search Results

It is widely accepted that engine combustion is fundamentally affected by the in-cylinder charge motion. Flow field structures present at the time and location of spark ignition are known to have a controlling effect on early flame development. Therefore, improved understanding of the variation in flow field structures local to the spark plug at the time of ignition is required. This study investigates the spatial and temporal development of flow field structures within the pent roof combustion chamber of a single cylinder, direct injection spark ignition (DISI) optical engine. High speed particle image velocimetry (HSPIV) has been used to quantify the flow field leading up to and following spark ignition. HSPIV data was recorded at a rate of 5 kHz, providing a temporal resolution of 1.8 crank angle degrees (CAD) between measurement fields and a spatial resolution of 512 by 512 pixels.

Recent pressures on vehicle manufacturers to reduce their average fleet levels of CO2 emissions have resulted in an increased drive to improve fuel economy and enable use of fuels developed from renewable sources that can achieve a net reduction in the CO2 output of each vehicle. The most popular choice for spark-ignition engines has been the blending of ethanol with gasoline, where the ethanol is derived either from agricultural or cellulosic sources such as sugar cane, corn or decomposed plant matter. However, other fuels, such as butanol, have also arisen as potential candidates due to their similarities to gasoline, e.g. higher energy density than ethanol. To extract the maximum benefits from these new fuels through optimized engine design and calibration, an understanding of the behaviour of these fuels in modern engines is necessary.

In an attempt to study the numerous contributors towards cyclic variations in combustion in a direct injection spark ignition engine, simultaneous high-speed imaging of fuel injection and flame growth are undertaken on a crank-angle resolved basis in a single-cylinder optical research engine. Batches of images from 100 consecutive cycles are acquired for all conditions with synchronised in-cylinder pressure logging. The engine is motored and fired at stoichiometric conditions at 1500 RPM under part-load and wide-open-throttle conditions (0.5-1.0 bar intake pressure), with injection timing set early in the intake stroke to promote homogeneous mixture formation with a centrally mounted multi-hole injector. Liquid impingement is observed on the cylinder walls and on the piston crown with early intake injection and multiple injection strategies are employed in an attempt to reduce impingement and alter mixture preparation and subsequent combustion.