The effect of multi-hole injector, EGR and pilot injection is studied on the purpose of reducing the particulate matter (PM) and nitrogen oxides (NOx) emissions in a high speed direct-injection (HSDI) diesel engine. Multi-hole injector could lead faster atomization and vaporization due to the small hole-diameter. It increases the portion of the premixed combustion, which results in low PM emission. Adversely, NOx emission increases due to the rise of the combustion temperature with enhancement of the airfuel mixing. EGR could be applied to resolve this problem. In addition, pilot injection could compensate power output and assist NOx reduction.
The main objective of this study is to investigate the effects of the combined use of EGR and optimized pilot injections with multi-hole injector on combustion and emissions. The study was carried out in a single-cylinder optical direct-injection (DI) diesel engine equipped with a high pressure common-rail fuel injection system. Tests were performed at fixed engine speed (800 rpm) with variations of the EGR rate and the injection pressure. Two different injectors with 5 and 14 holes were tested. EGR rate was applied from 0 % to 50 %, and pilot injection test was performed under the same condition. The experimental results showed that 14-hole injector achieved better combustion performance, while it increased NOx emission at 60 MPa injection pressure. EGR reduced NOx emission by 80~90 % without a significant increase in PM emission. The reduction of flame luminosity through the visualized combustion explained these phenomena. The optimized use of multi-hole injector, EGR and pilot injection showed the improved power output and the reduced NOx and PM emissions.
고압 분사와 함께 분사기의 분공수를 증가시키면, 연료의 미립화와 공기와의 혼합이 개선되어 연소성능이 향상되고 PM 이 줄어드는 효과를 얻을 수 있다. 그러나 이와 함께 또한 NOx 생성량이 증가하게 된다. 이러한 NOx와 PM 의 Trade-off 문제를 해결하기 위해 EGR, 다공분사와 함께 파일럿 분사 방법을 적용한다면 NOx와 PM 의 동시 저감은 물론 출력까지 향상 시킬 수 있게 된다. 본 연구에서는 커먼레일 분사 시스템을 장착한 직접 분사식 단기통 디젤엔진을 이용하여 분공수 변화에 따른 영향과 함께 분공수 증가로 인한 단점을 보완하기 위해 배기가스 재순환(EGR)과 파일럿 분사 기법을 동시에 적용하였을 경우 연소 과정과 공해 배출물의 형성에 미치는 영향에 관해 알아보았다.
