Conversion of a single-cylinder internal combustion engine to dual-mode homogeneous charge compression ignition engine

Homogeneous charge compression ignition (HCCI) technology has been a forerunner in improving efficiency and reducing emissions in conventional internal combustion engines. Despite significant research activity in the past few decades, engines operating on HCCI technology have not been commercially successful owing to practical engineering challenges. The current study attempts to convert a single-cylinder agricultural diesel engine to a gasoline HCCI mode. Dual mode of operation was employed to overcome the shortcomings of HCCI technology. The control algorithms were designed to switch between the gasoline HCCI mode and the diesel DI (direct injection) mode depending on load. A numerical simulation strategy was deduced to determine the initial experimental conditions. The HCCI mode could not be sustained above 40% load with the current control strategy which corresponds to 1.49 kW of brake power. In HCCI mode, a brake thermal efficiency of 23%, NO_x emissions of 1.4 g/kW h, and CO₂ emissions of 2200 g/kW h were achieved which was an improvement of approximately 15%, 80%, and 30%, respectively, at comparable loads in DI mode. Reduction in engine-out NO_x is an attractive feature of HCCI engines. However, at lower loads CO and HC emissions of 1600 g/kW h and 46 g/kW h were achieved which were higher than conventional diesel DI mode and would be tackled by after-treatment systems which are economical as compared to after-treatment of other air pollutants. Overall, the technology was found to be clean and economically viable. Modifications to achieve dual-mode operation holds a potential to commercialize it, as it can be cross-deployed in any engine of similar class, which is an important feature considering the impact of these engines on air quality and economy of a country.