Experimental investigation of the impact of post-injection on emissions, combustion and lubricant dilution in a diesel engine with B20 fuel

Abstract

A 100 hour (h) engine experiment was conducted to investigate the impact of post-injection strategy on emissions, combustion and lubricant dilution with a common-rail turbocharged direct-injection diesel engine at moderate speed and low load. The fuel was a B20 v/v blend of a soybean methyl ester-based biodiesel and ultra low sulfur diesel. The impacts of post-injection on engine performance and emissions were investigated. The total acid number of the lubricant, the engine mechanical friction mean effective pressure and hydrocarbon components in both the exhaust gases and the used lubricant were analyzed. The variations of engine performance strongly depended on the timing of the post-injection. The key parameter that controlled the combustion process of post-injected fuel at late crank angle (later than 40° after top dead center) was found to be the cylinder temperature at which the post-injected fuel was about to ignite. The bulk cylinder temperature threshold was confirmed to be 1500 K, below which a rapid combustion of injected fuel was not observed. The vaporized components of the post-injected fuel were found to contribute the majority of the significantly increased unburned hydrocarbon emissions with the post-injection strategy. Furthermore, these unburned hydrocarbons were also found to be the primary source for lubricant dilution.