For over a century in the history of internal combustion engines, two concepts have played a dominant role during the process of development and production. The spark ignition or gasoline engine shows the distinctive feature of high specific power and large speed range due to its good level of air utilisation; whilst the compression ignition or Diesel engine, offers better thermal efficiency from the use of a higher compression ratio, and the absence of throttling. Combining the positive aspects of these two engine types has always been a goal of engine research and development in the automobile industry, and Gasoline Direct Injection (GDI) Spark Ignition engine is seen as one of the most promising ways to achieve this aim.
The following aspects of GDI engine operation have been investigated at Oxford:
Paul Ewart, Ben Williams, Felix Leach Joe Camm (and previously: Lukas Wyszynski, Rob Stevens, Hongrui Ma, Xiaowei Wang, Ben Twiney, Fan Xu, Longfei Chen, Mike Braisher
Since 2004 we have been using an optical access engine that has the Jaguar AJ-V8 Gen III Engine Combustion System, subsequently this was complemented by a prototype of the V8 engine. Optical access is via a piston window, annulus and a pent-roof window in the cylinder head.
Spray imaging uses a pulsed LED illumination system and a high speed video camera that also films the combustion process. The grey scale image of the fuel spray is false-coloured so as to facilitate visual comparisons, but integration can also be used to track the evolution and dispersion of the spray. Quantitative Planar Laser Induced Fluorescence (PLIF) has been used to determine the air/fuel ratio (AFR) distribution. Three different tracers (acetone, toluene and trimethylbenzene) have been used with a fuel that has light medium and heavy fractions that co-evaporate with each of the tracers.
If the video camera has a spectral calibration for its colour filter array then colour ratio pyrometry can be used to quantify the temperature and quantity of soot present in the burned gas.