Experimental Study On N-heptane Fueled Compound Combustion Engine Using Port/Direct Injection

The compound combustion in an n-heptane fueled engine, based on port/direct injection has been investigated. The performance of combustion and emissions have been discussed by changing the rate of port injection and the direct injection timing, which has been set at the cool flame timing of the premixed combustion (θ= -23°ATDC), the main combustion timing of the premixed combustion (θ= -13°ATDC), and the end of the premixed combustion (θ= -3°ATDC). It was found that varying the direct injection timing influenced the combustion performance. With earlier direct injection timing, It was found 2 phases heat release, while with later direct injection timing, there were 3 phases heat release. The main combustion of the premixed combustion and the diffusion combustion of the direct injection started together when direct injected at an earlier timing; and at the later direct injection timing, they separated. The effect on the rate of heat release by changing the rate of port injection has been discussed too. The resulting emissions shows that comparing to premixed injection, the port/direct injection has advantages in HC and CO emissions and has lower NOx emission than direct injection. HC and CO emissions were relation with the quantity of direct injection, while the NOx emission was determined by the direct injection timing. The combustion stability was also investigated. It shown that with earlier direct injection, at lower load, the compound combustion strategy had better ignition performance than premixed combustion strategy, while had a better NOx emission than direct injection combustion strategy; and with later direct injection, at high load, use port/direct injection strategy can bring a more stability combustion than premixed combustion and a better NOx emission than direct injection combustion strategy.