Effect of Premixed Ratio of Gasoline on Emissions and Performance Characteristics of a Dual Fuel Mode HCCI Engine
HCCI combustion is a concept of hybrid combustion between the Otto cycle based SI engine and Diesel cycle based CI engine combustion mechanisms. Higher engine efficiency coupled with lower emissions of NOX and particulate matters are the benefits of HCCI engines. However, there are a few challenges in HCCI operation, such as low specific output, narrow operating range, lack of control over the ignition process, long startup time and more emissions in case of CO and UHC. To overcome these challenges, different methods of fuel supply such as blends, multiple fuel injection, dual fuel mode, fumigation, additives are suggested. Narrow operating range is the main concern in HCCI engine. To increase the operating range, dual fuel method is incorporated in this study. In this method, two reactive fuels are supplied to the engine separately; one fuel is passed through the carburettor and another direct injection. Due to the difference in the auto-ignition temperatures of the two fuels, the engine is able to perform at high load condition. Thus, the present work is aimed to reduce the NOX and smoke opacity emissions by using two different fuels at a different location with an increased operating range of HCCI engine.
The experiments were conducted at a constant speed (1500 rpm) for varying loads such as 0%, 20%, 40%, 60%, 80% and 100% for the different premixed ratio of gasoline and diesel. Further experiments were conducted for the optimization of a premixed ratio on the basis of maximum thermal efficiency by using different fuel jets in the carburettor. The results show that engine NOX and smoke opacity emission was reduced with increasing premixed ratio of gasoline at the given range of load, but HC and CO emissions were increased.