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