Ignition timing control at Toyota UNIBUS combustion system

Several approaches are being taken to develop new combustion systems for drastic reductions of nitrogen oxide and soot emissions from diesel engines, while remarkably increasing fuel economy. The most promising approach is one in which a proper combustion structure is provided with a premixed compression ignition system. The author et al. proposed a new system named UNIBUS (Uniform Bulky combustion System). The image of combustion was taken by shadow graph method, and an image intensifier was used to detect very weak photic signals in combustion. The level of NO x is about 1/100 that of a conventional DI diesel engine. The mechanism of extremely low NO x and the onset of ignition were discussed. The study revealed that a new combustion process can be established by promoting fuel dispersion before ignition. The prereaction prior to combustion was intensively discussed from the aspects of mixture formation and chemical reaction. The chemical reactions such as from low temperature oxidation to high temperature oxidation which occur due to the gas temperature changing in engine, were determined by analyzing the combustion images and the heat release patterns. Furthermore, in application of the concept to engines with the usual Common Rail injection system and hole type nozzle, the new idea of ignition timing controlling was introduced additionally in the original concept.