Effect of pilot quantity on combustion and emission characteristics of a single-cylinder diesel engine under fixed dwell condition: experimental and numerical study

Abstract

Dwell and distribution of fuel quantity between two injection pulses are the most important parameters under pilot injection mode used in diesel engines. Most of the earlier studies have studied the effects of pilot fuel quantity (herein referred as pilot quantity) on diesel engine combustion at fixed pilot and main injection timings. Hence, results obtained represent the combined effects of dwell and pilot quantity. Aim of the present study is to investigate the sole effect of pilot quantity on combustion and emission characteristics of a diesel engine at a fixed dwell using experimental and simulation tools. Pilot injection timing was adjusted in order to maintain a constant dwell between pilot and main injection with varying pilot quantity, while main injection timing was maintained constant during the study. Numerical investigations were also performed using Converge 3-D computational fluid dynamics tool. When pilot quantity was increased from 15 to 45%, smoke emissions were reduced by 25%, while nitric oxide (NO) emission and fuel consumption were increased by 20.8% and 2.52%, respectively. Greater amount of fuel participating in pre-mixed combustion proportion in case of larger pilot quantity led to overall lesser smoke emissions compared to smaller pilot quantity case. Numerical results confirmed that prime source of soot emissions in case of pilot injection mode is the main injected fuel. Higher NO emission in case of larger pilot quantity is mainly attributed to the presence of greater and wider high-temperature region (HTR) compared to smaller pilot quantity case. Increased fuel consumption with increasing pilot quantity is mainly due to deteriorated space utilization.