Date of Award


Publication Type

Master Thesis

Degree Name



Mechanical, Automotive, and Materials Engineering


Lean-Burn; SI Engine Efficiency; Spark Ignition; Swirl


Zheng, Ming


Reader, Graham




As stricter emission and fuel efficiency regulations continue to be set forth by government regulating bodies, the need to optimize the gasoline engine and control every aspect of combustion has never been greater. Gasoline engines which utilize exhaust gas recirculation (EGR) and lean-burn combustion systems are attractive pathways which have shown potential in reaching these targets. However, due to the suppressed reactivity, the ability to ignite and completely burn the mixture is reduced and can lead to unstable operation. It is well established that increased in-cylinder air motion can improve the mixing and turbulence generation which in turn, increases the probability of ignition and the flame velocity. This work investigates the potential benefit of enhanced swirl motion, which is the rotation of charge about the cylinder axis, under lean engine operating conditions. The ultimate objective is to extend the lean-limit of combustion and increase the thermal efficiency. Steady flow tests were conducted on a cylinder head from a single-cylinder research engine using an in-house developed flow bench system. Swirl speeds were measured using a vane-type swirl meter. Computational fluid dynamics (CFD) simulations were conducted to investigate different intake geometries to enhance the swirl motion. The intake runner geometry which produced an increase in the swirl speed was tested on the flow bench. The steady-flow results showed an increase in the swirl ratio over the baseline measurements. Finally, engine tests were conducted to investigate the effect of the enhanced swirl. The engine test results demonstrated that the lean limits were extended and the thermal efficiency was increased with the enhanced swirl.