Comparison of the indicated work outputs, idle stabilities, and heat release characteristics of a direct-injection diesel engine operating cold at two compression ratios

Abstract

A reduction in the compression ratio can adversely affect the cold-start and idling performance of diesel engines. The problems and potential solutions have been investigated. Studies have been carried out to compare the indicated performances and heat release characteristics of a direct-injection diesel engine during low-speed cold operation at compression ratios of 18.4:1 and 15.4:1. The test engine was a naturally aspirated single-cylinder design with a swept volume of 0.5 l. Tests covered start temperatures between 10 uC and 220 uC. At around 300 r/min, the indicated work output was higher at the lower compression ratio as a result of lower blow-by, and the cycle-by-cycle stabilities of the heat release and work output were similar at both compression ratios. The cycle-by-cycle stability deteriorated with increasing engine speed. At 1000 r/min idling conditions, the stability was relatively poor and was worse for the low-compression-ratio case. At the high compression ratio, the cycle-bycycle stability was improved by introducing multiple pilot injections and using metallic glow plugs operating at about 850 uC. At the low compression ratio, improvements in stability could not be achieved without switching to glow plugs operating at about 1100 uC.

CFD Investigation on the Influence of In-Cylinder Mixture Distribution from Multiple Pilot Injections on Cold Idle Behaviour of a Light Duty Diesel Engine

“…Various studies [1,2,3,5,6,7,8] have concluded that cold start performance can be greatly assisted by the introduction of a pilot injection, promoting cool flame reactions creating an activated environment in which to inject the main. To examine why extra pilot injections have a positive impact on heat release characteristics in-cylinder fuel distribution has been investigated using Kiva3v.…”

“…McGhee et al [2] pointed out the importance of an optimised injection strategy at cold idle conditions for low compression ratio HPCR diesel engines. Findings reported by Pacaud et al [3] and MacMillan et al [4,5] have highlighted the importance for further work to investigate cause of poor cold idle stability and the development of suitable techniques to make improvements. The importance of cool flame and hot pre-mixed combustion in promoting reliable combustion of fuel delivered in the main injection was indicated by Perrin et al [6].…”

“…Increasing the number of injector holes, for an equal nozzle flow rate, enhances the air entrainment assisting with fuel air mixing [7]. Previous work [5,8] has shown that the addition of multiple pilot injections is a key stabilising factor for cold start and idle operations. Heat release profiles suggest it ensures better mixture preparation and drastically reduces the negative impact on stability introduced by a bad cycle.…”

Investigating the impact of copper leaching on combustion characteristics and particulate emissions in HPCR diesel engines

“…The dynamometer was used to maintain the set point engine speed throughout the test. The use of a single cylinder research facility with dynamometer control allows detailed analysis of combustion events by eliminating variables such as engine speed and cylinder to cylinder variations/interactions, a technique previously applied by McGhee et al [30,31] and MacMillan et al [32]. Complete control over injection parameters was possible throughout the investigation.…”