Effect of novel fuel vaporiser technology on engine characteristics of partially premixed charge compression ignition (PCCI) engine with toroidal combustion chamber

Abstract

Partially pre-mixed charge compression ignition (PCCI) and combustion chamber geometry are significant factors that improve the potential of compression ignition engines and the sustainable effect on the environment. The considerable decline in brake thermal efficiency in PCCI has always been a point of halt in the progress of this technology. The toroidal combustion chamber (TCC) has proved its effectiveness in enhancing the performance characteristics of a conventional engine. The primary aim of this experiment is to improve the engine characteristics for PCCI mode when it operates with a TCC piston bowl geometry and compare the behavior with the conventional direct injection (DI) technology. A novel fuel vaporiser technology is developed and retrofitted in a single-cylinder DI diesel engine in this work. A comparative study on the effect of combustion chamber geometry (hemispherical and toroidal) on engine characteristics was performed and the engine setup was operated in conventional and PCCI mode. The PCCI mode was tested by using fuel vapour induction in intake manifold via the fuel vaporizer unit. Liquid diesel fuel was heated up to its vaporization temperature and sent to the intake manifold, wherein fresh air was mixed with vaporized fuel, forming an external mixture that enters the combustion chamber. The different vapour induction rates (2 ml/min and 4 ml/min) were used to understand the changes in combustion behavior. Compared to conventional, the PCCI mode proved its worth in limiting NOx emission with 7 g/kW-h reduction at 4 ml/min vapour induction rate with HCC at moderate engine load. Diesel vapour induction rate of 2 ml/min along with TCC piston resulted in improved engine characteristics with a marginal decrement in BTE by 1.2%, significant decrease of NOx by 5 g/kW-h at moderate engine load. Moreover, at full engine load, the PCCI anomaly is observed as the rate of pressure rise (ROPR) surpasses the conventional by 2 bar/deg for 2 ml/min induction rate with HCC, thereby favouring conditions for engine knock. Overall, the brake thermal efficiency limitations in PCCI can be countered by TCC piston bowl geometry; however, the PCCI usage is limited to a specific vapour flow rate and engine load range.