Osborne, R., Downes, T., O'Brien, S., Pendlebury, K. et al., "A Miller Cycle Engine without Compromise - The Magma Concept," SAE Int. J. Engines 10(3):2017, doi:10.4271/2017-01-0642.
The Magma engine concept is characterised by a high compression ratio, central injector combustion system employed in a downsized direct-injection gasoline engine. An advanced boosting system and Miller cycle intake-valve closing strategies are used to control combustion knock while maintaining specific performance. A key feature of the Magma concept is the use of high CR without compromise to mainstream full-load performance levels. This paper focuses on development of the Magma combustion system using a single-cylinder engine, including valve event, air motion and injection strategies.Key findings are that Early Intake Valve Closing (EIVC) is effective both in mitigating knock and improving fuel consumption. A Net Indicated Mean Effective Pressure (NIMEP) equivalent to 23.6 bar Brake Mean Effective Pressure (BMEP) on a multi-cylinder engine has been achieved with a geometric compression ratio of 13:1.Comparison of weighted key point cycle predictions for the downsized Magma concept vs a contemporary baseline engine, indicates fuel consumption savings over WLTC and FTP-75 of 12.5% and 16.4% respectively.The cost / benefit trade-off is currently being refined, but the position in terms of cost per gram per mile of CO2 benefit appears to favour a Magma solution over other options. Part of the benefit arises from the current assumption that a 2.0 litre L4 engine is replaced with a 1.5 litre L3 which is enabled by the higher specific rating of the Magma concept. The reduction in base engine cost offsets some of the additional air handling equipment.