Parametric study and optimization of diesel engine operation for low emissions using different injectors

The objective of this research was to develop advanced diesel combustion strategies for emissions reduction in a multi-cylinder diesel engine. The engine was equipped with an electronically-controlled, common-rail fuel injection system, and an exhaust gas recirculation (EGR) system. This experimental setup allowed a wide range of operating conditions to be explored. Effects of various injector parameters with various EGR levels on emissions were studied. Injector parameters included the injector flow number, nozzle hole geometry (straight, convergent), and nozzle arrangement (6-hole, 10-hole, 16-hole). The included spray angle was kept constant at 133 deg. Other engine parameters included the EGR rate (0-41%), injection pressure (150-225 MPa), start of injection (SOI) (-20 to 5 ATDC), start of pilot injection (-40 to -15 ATDC), and pilot fuel percentage (0-25%). For single injection operations, a simultaneous reduction of NOx and particulate matter (PM) was achieved by using high EGR (30%) with late injection timing (0 to 5 ATDC) at high injection pressures (150 MPa). For double injection operations, NOx and PM emissions were reduced using 30% EGR, 15% pilot injection at an early pilot timing (-30 ATDC) and late main injection (5 ATDC). Injectors with low flow numbers were able to produce low emissions at high EGR levels (>35%) and high injection pressures (>150 MPa). The combustion was stable at these high EGR levels as the SOI was held at 0 ATDC. On the other hand, injectors with high flow numbers were not able to produce stable combustion at such high EGR levels with late SOI.