Innumerable procedures are being taken to intensify newcombustion system for exorbitant reduction of nitrogen oxide and unrefined sootemissions from diesel engines, while there is substantial increase in fueleconomy. An idealized combustion structure, which is equipped with a premixed compressionignition system is found to be one of the most promising approach. A newcombustion system named UNIBUS(Uniform Bulky combustion System) was proposed bythe author et al. In UNIBUS image of combustion was taken by shadowgraphmethod, and an image intensifier was employed to detect very weak photicsignals in combustion. These images were used to analyze the gas temperaturechanging in the engines, which triggers the chemical reactions such as lowtemperature oxidation to high temperature oxidation.The NOx level of about 1/100, that of a conventional directinjection diesel engine was achieved through a range of injection timing. This mechanism had outrageously low NOx.
The study disclosedthat a new combustion process could be justified by promoting fuel dispersionbefore ignition. The concept called Trigger of Ignition was made known inUNIBUS, to control ignition through the predominant common rail injection inthe manufacturing engines. There would be a chance to build up time period ifthe mixtures in some parts play as a trigger of ignition, which leads to themixture attaining Homogeneity.The heat-released rate in the UNIBUS was found to have two-heatrelease rate peak, while the conventional diesel combustion system provided oneheat release peak. The reason for this was found to be, the extend to which theinjection timing was fostered, that is, the degree of fuel dispersion and thesurrounding gas temperature.It is challenging to achieve the homogeneous mixture in ahigher engine speed operation conditions.
The micro hole nozzle is reliablesolution for the above problem. The increased number of holes and reducing thenozzle hole size showed good proclivity for improving mixture in the enginetest.It was verified by the engine test that low pollutantemissions and low noise characteristics were achieved in UNIBUS.