Thermal efficiency of a dual-mode turbulent jet ignition engine under lean and near-stoichiometric operation

Abstract

Turbulent jet ignition is a combustion technology that can offer higher thermal efficiency compared to the homogeneous spark ignition engines. A potential combustion-related challenge with turbulent jet ignition is the pre-chamber misfiring due to improperly scavenged combustion residuals and maintaining the mixture composition there. Dual-mode turbulent jet ignition is a novel combustion technology developed to address the aforementioned issues. The dual-mode turbulent jet ignition is an engine combustion technology wherein an auxiliary air supply apart from an auxiliary fuel injection is provided into the pre-chamber. This technology can offer enhanced stoichiometry control and combustion stability in the pre-chamber and subsequently combustion control in the main chamber. In this work, engine testing of a single-cylinder dual-mode turbulent jet ignition engine having a compression ratio of 12.0 was completed with liquid gasoline and the indicated thermal efficiency was measured. High-speed pressure recordings were used to compare and analyze different operating conditions. Coefficient of variation in the indicated mean effective pressure and the global air/fuel equivalence ratio values were used to characterize the engine operation. Lean operating conditions for a global air/fuel equivalence ratio of 1.85 showed an indicated efficiency of 46.8% ± 0.5% at 1500 r/min and 6.0 bar indicated mean effective pressure. In addition, the combustion stability of this engine was tested with nitrogen dilution. The nitrogen diluent fraction was controlled by monitoring the intake oxygen fraction. The dual-mode turbulent jet ignition engine of compression ratio 12.0 delivered an indicated efficiency of 46.6% ± 0.5% under near-stoichiometric operation at 1500 r/min and 7.7 bar indicated mean effective pressure with a coefficient of variation in indicated mean effective pressure of less than 2% for all conditions tested.