Optimization of Lambda Across the Engine Map for the Purpose of Maximizing Thermal Efficiency of a Jet Ignition Engine 2020-01-0278
Progressively more stringent efficiency and emissions regulations for internal combustion engines have led to growing interest in advanced combustion concepts for spark ignition engines. MAHLE Jet Ignition® is one such concept which enables ultra-lean (λ > ~1.6) combustion via air dilution. This pre-chamber-based combustion system has demonstrated highly efficient lean operation, competitive with advanced compression ignition concepts. Compared to a traditional spark ignition engine, the additional degrees of freedom associated with Jet Ignition introduce a further degree of complexity when optimizing the system for peak efficiency throughout the engine map. The relationship between operating condition and the lambda at which peak efficiency occurs for a Jet Ignition engine has been presented in prior work by the authors. This paper further explores this complex relationship, introducing new interdependencies which must be considered in order to improve brake thermal efficiency (BTE).
Experimental data is obtained from a 1.5L 3-cylinder gasoline-fueled Jet Ignition engine. An engine map of BTE is presented. An in-depth analysis at several key points throughout the engine map shows how certain parameters are adjusted to optimize BTE, providing a peak value >42%. A first law thermodynamic analysis is performed for lambda sweeps at these points, emphasizing the important loss pathways at different locations throughout the map. Further insight into the factors affecting efficiency is provided through parameter sweeps of pre-chamber fuel and analysis of high-speed pressure traces. The impact of precise fuel metering on BTE and combustion stability is highlighted. Finally, an investigation of high load operating points elucidates the relationship between Jet Ignition and the boost system near the knock limit as well as the benefits and challenges associated with ultra-lean operation at these points.
Nathan Peters, Sai Krishna Pothuraju Subramanyam, Michael Bunce, Hugh Blaxill, Adrian Cooper