Computational and Experimental Development of Novel Combustion Strategies for Advanced Internal Combustion Engines

Fuel lean combustion strategies are attractive methods to increase the thermal efficiency of gasoline, spark ignition, internal combustion engines, but engine design remains challenging due to the lean flammability limits of the fuel/air mixture. Turbulent jet ignition originating from a pre-chamber can help address mixture flammability limits by ejecting high enthalpy and highly reactive jets into the main combustion chamber, enabling overall lean combustion. Appropriate mixture conditions must be achieved in the main combustion chamber as well as in the pre-chamber for this strategy to be successful. This dissertation study considered a series of experimental and computational efforts to support the development of lean burn reciprocating engines. Fundamental combustion experiments to quantify flame speeds, flammability limits, and the interaction between flames and auto-ignition events of lean iso-octane /air mixtures were performed at premixed, moderate temperature and pressure conditions in a rapid compression facility. The results provided the first measurements of lean flammability limits at conditions relevant to spark ignition engines. Next, computational fluid dynamics was used to evaluate six prototype engine configurations with the goal of achieving ignitable, near-stoichiometric, fuel-to-air equivalence ratios in two indirectly fueled pre-chambers, while simultaneously achieving fuel lean equivalence ratios in the main combustion chamber. The simulation results showed the final iteration achieved the design goals with good flexibility in the fuel injection strategies. In the next stage of the project, optically accessible engine hardware was produced based on the CFD results to evaluate the fuel and air flow motion. High speed cinematography and pressure diagnostics were used with a fully-transparent cylinder liner to illuminate and image the fuel spray and air charge motion using Mie scattering. The fuel flow motion was in agreement with CFD predictions and the air charge imaging confirmed vortices were developed near the surface of the piston. The fuel spray data are the first in situ measurements of the unique fueling strategy and unique hardware. The combination of fundamental experiments, computational studies and applied experimental validations have demonstrated a new process and new outcomes for combustion science and technology that can operate significantly more fuel lean than traditional spark ignition engines.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135834/1/dassanis_1.pd