Critical review on the characteristics of performance, combustion and emissions of PCCI engine controlled by early injection strategy based on narrow-angle direct injection (NADI)

Stricter regulations on emissions from diesel engines have shifted the conventional combustion to more advanced combustion, aiming to minimize the emissions of NOx and PM. It is believed that it is possible to simultaneously reduce emissions of NOx and PM in diesel engines by applying combustion modes based on either partially premixed compression ignition strategy (PPCI) or premixed charge compression ignition strategy (PCCI). Normally, PCCI/PPCI combustion modes are able to be achieved by employing early injection timing to increase the time available for mixing fuel and air in order to control the combustion phase. Unfortunately, overearly injection timing can lead to the fuel spray missing the piston bowl causing a significant increase in emissions of PM, HC, and CO. The solution given out for early direct injection (EDI) strategy in PCCI combustion condition to overcome high emissions of PM, HC, and CO is the use of narrow-angle direct injection (NADI) to target the fuel spray toward the piston bowl aiming to reduce the wall wetting and fuel spray impingement. Therefore, the main goal of this review work is to evaluate the effects of NADI on the performance, combustion and emission characteristics of diesel engines operated under advanced injection timing-based PCCI combustion mode in comparison to those of conventional combustion.