Influence of injector spray angle and gasoline-diesel blending ratio on the low load operation in a gasoline compression ignition (GCI) engine

Advanced compression ignition (CI) engines relying on advanced combustion mode as partially premixed combustion (PPC) own potential for achieving efficient and clean operations. High octane fuels were identified as the most suitable propellant for such advanced CI engines. However, the high Octane Number (ON) of commercial gasoline limits the lowest achievable load under CI conditions. Increasing gasoline fuel reactivity at low load condition is a solution to overcome gasoline partially premixed combustion (PPC) issues at low load. This work reports the results of running a CI engine with such of three fuel blends: neat gasoline (G100) and two gasoline-diesel blends with a diesel content of 10% (G90) and 20% (G80). To investigate typical low load conditions, a fixed mass of 20 mg/cycle was delivered for all the fuels tested. For all the fuels, test were performed by using the custom 146° (UA146) umbrella angle diesel injector and a second injector with a 70° umbrella angle (UA70) . Ignition delay calculation were performed to support analysis of the results from the experiments. Results showed that improving the local mixture strength by using the narrower UA70 injector allowed to achieve gasoline auto-ignition without boosting or intake air heaters. Despite the low soot and nitrogen oxides (NOx) emission, gasoline combustion led to high CO and HC emissions. In the UA70 case, improving fuel reactivity by increasing the diesel content of the blend led to an increase of soot emissions without a substantial benefit in terms of CO and HC emissions. With the custom UA146 injector, reducing the ON by using the G90 and G80 fuel blends was necessary to achieve stable combustion. As a conclusion, results from experiments showed that the best fuel-injector combination for efficient low load operation with low emissions of NOx and Soot was provided by the UA146 injector and G90 blend.