Premixed Lean Diesel Combustion (PREDIC) has very low NOx combustion because of early injection timing, for example, at -120 degrees ATDC; however, it has some problems. One problem is that so much fuel spray reaches the cylinder wall, which causes high HC emission and high fuel consumption. The other problem is that compression ignition timing control is difficult due to the dependence on the in-cylinder temperature. To solve these problems, an impingement spray system with two nozzles is attempted to obtain the spray increasing at the center of the combustion chamber instantaneously. This impingement spray system has two nozzles, which are located diagonally. Two sprays, one injected from each side injector, impinge each other at the center of the cylinder to create an air-fuel mixture.That is,this impingement spray system creates the air-fuel mixture by using the penetration of both sides of the sprays instead of early timing injection.
According to our previous study, using a high-pressure vessel, the air-fuel mixture is shaped at the center of the two nozzles, and its volume grows larger than that of a free spray on the same time scale, which means a higher local air-fuel mixture. Also, according to our previous study using a single-cylinder engine, HC reduction and fuel consumption improvement are obtained.
In this study, we applied this system to PREDIC using a heavy-duty single cylinder engine with direct water injection, and evaluated the combustion controllability by water latent heat and thermal efficiency improvement by water vapor atmosphere for an adiabatic effect. As a result, we find that adequate water injection with the impingemnt spray of a split injection pattern can retard fuel injection timing by keeping low NOx and low HC emission levels, whose timing is more retarded than that of PREDIC.
The above results show that the system is one of the answers for NOx and HC simultaneous reduction and fuel consumption improvement, and that it had a possibility of controlling ignition timing in PREDIC.