Optimizing Valve Timing and Swirl Ratio for Emission Mitigation in Small Single-Cylinder Diesel Engines

Small diesel engines are widely used for commercial vehicle and passenger car applications due to their higher torque requirements, fuel economy, and better thermal efficiency. These engines are exposed to different operating and environmental conditions and hence emissions from these engines are erratic. Strategies are required to enhance performance and reduce engine-out emissions considering environmental pollution and regulations. The main objective of this experimental study is to develop strategies for performance improvement and emission reduction for naturally aspirated engines, which can further be used for emission reduction of the multicylinder engine. Experimental work has been carried out on a single-cylinder naturally aspirated diesel engine to study the impact of engine operating parameters like valve timing, swirl ratio, and injection pressure on engine performance and emissions. Parameters considered for the study are: three intake valve opening timings, two fuel injection pump pressures, two-cylinder head swirls, and three start of injection timings. Results showed improvement in performance, lower exhaust gas temperature, and reduction of engine-out emission. Exhaust gas temperature was reduced by 5-18% with advanced valve opening and lower cylinder head swirl option. NOx emission was reduced by 5-50% at advanced intake valve opening (IVO) options with retarded start of injection (SOI) and lower swirl cylinder head. This has a penalty on CO and HC emissions since the availability of fresh air is less due to higher internal exhaust gas recirculation (EGR). Higher pressure fuel injection pump helps in improving engine torque with an adverse effect on engine-out NOx emission. As these engines are of low power capacity segment and are used in few countries, research on these engines is limited. All research work has been carried out in the field of intake valve closing timings, swirl ratio and injection timings; however, very limited research is available for the effect of intake valve opening timings due to practical limitations of the lower valve to piston clearance in diesel engines.