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The air flow velocity field in an internal combustion engine is fundamentally involved in all aspects of the combustion process, broadly affecting engine performance, including fuel economy, stability, heat release rates, and exhaust emission. Unfortunately, common and advanced methods used to design engine surface geometries which control this velocity field typically rely on simple non-reacting models which fail to reflect true complex combustion behaviors. An alternative but presently undeveloped approach which could overcome this challenge, is to integrate shape optimization, additive manufacturing, and firing engine experiments in a process which creates designs driven directly by engine performance measurements and targets. In this work, an initial experimental approach to the shape optimization of a tumble-inducing orifice within an internal combustion engine intake runner was developed and demonstrated.

The majority of engine out particulate emissions are released in the first several minutes of cold start operation, in large part due to cold piston surface temperatures which fall well below the boiling point of the injected fuel. Use of topology optimization methods to increase piston surface temperatures is a promising approach to solve this challenge, but existing applications have focused largely on basic small-scale canonical scenarios in the steady-state. In this work an algorithm was developed and demonstrated which is aimed at optimizing the internal structure of an engine piston to increase piston surface temperatures during the early phases of engine cold start, while subjected to a peak temperature limit during hot steady-state conditions. Finite difference heat transfer models of a light duty aluminum engine piston were created and an evolutionary optimization algorithm in conjunction with the Lagrange Multiplier Method were used to develop optimal piston topologies.

Non-reacting spray behaviors of the Engine Combustion Network “Spray G” gasoline fuel injector were investigated at flash and non-flash boiling conditions in an optically accessible single cylinder engine and a constant volume spray chamber. High-speed Mie-scattering imaging was used to determine transient liquid-phase spray penetration distances and observe general spray behaviors. The standardized “G2” and “G3” test conditions recommended by the Engine Combustion Network were matched in this work and the fuel was pure iso-octane. Results from the constant volume chamber represented the zero (stationary piston) engine speed condition and single cylinder engine speeds ranged from 300 to 2,000 RPM. As expected, the present results indicated the general spray behaviors differed significantly between the spray chamber and engine. The differences must be thoughtfully considered when applying spray chamber results to guide spray model development for engine applications.

The effects of aromatic content and octane rating of gasoline fuels on stochastic pre-ignition (SPI) behaviors were investigated at typical operating conditions using a modern 2.0 L turbocharged engine. In-cylinder pressure time history measurements made during a speed-load test sequence designed to stimulate SPI were used to determine both the frequency of SPI occurrence and the in-cylinder peak pressure during such events. Six fuels were tested with varying levels of aromatic content (15 - 35% by vol.) and two octane rating levels (∼88 & 94 anti-knock index). The engine was operated using a production-intent calibration with equivalence ratio near one. Pressure and temperature in the intake manifold were held constant near two bar and 35°C respectively. Significant SPI activity was observed, with abnormal event frequencies up to ∼1 SPI event per 1,000 engine cycles and in-cylinder peak pressures up to ∼200 bar.