Experimental investigation of combustion stability and nano-particle emission in conventional and advanced dual fuel compression ignition engine

Abstract

Dual-fuel operation in a CI-engine is a promising way for in-cylinder reduction of NOx and soot emission while having similar or higher fuel conversion efficiency as compared to conventional diesel engines. The in-cylinder blending of two fuels of different reactivity in CI-engine is typically known as dual fuel operation in CI-engine. Based on the fuel injection strategy and level of charge stratification, dual-fuel combustion mode is categorized into two types, i.e., conventional dual fuel CI engine and premixed reactivity controlled compression ignition (RCCI) engine. Present work mainly focused on the nano-particle emissions characterization and combustion stability analysis for conventional as well as advanced dual-fuel CI-engine (RCCI engine) along with their performance and combustion analysis. In this work, two different experimental setups are used to test an engine in conventional dual fuel and RCCI combustion mode. To operate both the engines in dual-fuel combustion modes, an intake manifold of the engine is modified, and a solenoid injector is installed in the intake manifold of the engine for injecting the low reactivity fuel. For conventional dual fuel CI-engine test rig, a separate port fuel injector controller is developed and used for injecting the required quantity of fuel in the intake manifold. For RCCI engine test rig, a development ECU is used for controlling the port as well as direct fuel injection events. The analysis of conventional dual fuel CI-engine commenced with the investigation of the effect of fuel premixing ratio (on an energy basis), compression ratio and diesel injection timing on the combustion stability and nano-particle emissions along with combustion and gaseous emission characteristics. The results indicate the range of fuel premixing is limited by higher cyclic combustion variations and unburned hydrocarbon emissions. At lower compression ratio operation, the range of the fuel premixing is very limited. Premixing of high octane fuel leads to increase the carbon monoxide and unburned hydrocarbon emission while the nitrogen oxide emissions decrease significantly. The nucleation mode particles are dominating in dual-fuel CI-engine. The nucleation mode particles increase with an increase in the fuel premixing ratio, while accumulation mode particle significantly decreases. The analysis of RCCI engine is commenced with the investigation of the influence of diesel injection strategy on the combustion stability and nano-particle emission characteristics of gasoline-diesel and methanol-diesel RCCI engine. Results depict too advanced high diesel injection timings (60° bTDC in gasoline and 40° bTDC in methanol RCCI operation) result in misfire/very high cyclic combustion variations. It has been found that the double injection strategy is an effective way to reduce the cyclic variations in the RCCI engine. In RCCI combustion, nucleation mode particles are also dominating and nucleation as well as accumulation mode particle peak, increases with an increase in the port fuel injected mass. Additionally, advanced diesel injection timing leads to an increase in the nucleation as well as accumulation mode particles. Based on operating and combustion parameters, empirical models are developed using regression analysis, which shows a good correlation for the estimation of particle number characteristics. These parameters can be used for prediction, control, and model development for particle emission in RCCI engine.