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RNG k-ε closure turbulence dissipation equations are evaluated employing the CFD code KIVA-3V Release 2. The numerical evaluations start by considering simple jet flows, including incompressible air jets and compressible helium jets. The results show that the RNG closure turbulence model predicts lower jet tip penetration than the "standard" k-ε model, as well as being lower than experimental data. The reason is found to be that the turbulence kinetic energy is dissipated too slowly in the downstream region near the jet nozzle exit. In this case, the over-predicted R term in RNG model becomes a sink of dissipation in the ε-equation. As a second step, the RNG turbulence closure dissipation models are further tested in complex engine flows to compare against the measured evolution of turbulence kinetic energy, and an estimate of its dissipation rate, during both the compression and expansion processes.

Several diffusion combustion scaling models were experimentally tested in two geometrically similar single-cylinder diesel engines with a bore diameter ratio of 1.7. Assuming that the engines have the same in-cylinder thermodynamic conditions and equivalence ratio, the combustion models primarily change the fuel injection pressure and engine speed in order to attain similar performance and emissions. The models tested include an extended scaling model, which scales diffusion flame lift-off length and jet spray penetration; a simple scaling model, which only scales spray penetration at equal mean piston speed; and a same speed scaling model, which holds crankshaft rotational velocity constant while also scaling spray penetration. Successfully scaling diffusion combustion proved difficult to accomplish because of apparent differences that remained in the fuel-air mixing and heat transfer processes.

The post-flame oxidation of unburned hydrocarbons released from the ring-pack crevice was investigated for a small, air-cooled, spark-ignition utility engine. Spark timing sweeps were performed at 50, 75 and 100% load and speeds of 1800, 2400 and 3060 RPM while operating at a 12:1 air-fuel ratio, which is typical for these engines. A global HC consumption rate (GCR) was introduced based on the temporal profile of the mass released from the ring pack; the mass release after CA90 and up to the point where the remainder of the ring pack HC mass is equal to the exhaust HC level was taken as the mass oxidized, and a rate was defined based on this mass and the corresponding crank angle period over which this took place. For all conditions tested, the GCR varied with the spark timing; advanced spark timing gave higher GCR.

A vaporization model for realistic multi-component fuel sprays is described. The equilibrium at the interface between liquid droplets and the surrounding gas is obtained based on the UNIFAC method, which considers non-ideal molecular interactions that can greatly enhance or suppress the vaporization of the components in the system compared to predictions from ideal mixing using Raoult's Law, especially for polar fuels. The present results using the UNIFAC method are shown to be able to capture the azeotropic behaviors of polar molecule blends, such as mixtures of benzene and ethanol, benzene and iso-propanol, and ethanol and water [1]. Predicted distillation curves of mixtures of ethanol and multi-component gasoline surrogates are compared to those from experiments, and the model gives good improvements on predictions of the distillation curves for initial ethanol volume fractions ranging from 0% to 100%.

The objective of this research is a detailed investigation of particulate sizing and number count from a spark-ignited, direct-injection (SIDI) engine at different operating conditions. The engine is a 549 [cc] single-cylinder, four-valve engine with a flat-top piston, fueled by Tier II EEE. A baseline engine operating condition, with a low number of particulates, was established and repeatability at this condition was ascertained. This baseline condition is specified as 2000 rpm, 320 kPa IMEP, 280 [°bTDC] end of injection (EOI), and 25 [°bTDC] ignition timing. The particle size distributions were recorded for particle sizes between 7 and 289 [nm]. The baseline particle size distribution was relatively flat, around 1E6 [dN/dlogDp], for particle diameters between 7 and 100 [nm], before dropping off to decreasing numbers at larger diameters. Distributions resulting from a matrix of different engine conditions were recorded.

An investigation of high speed direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline (termed GDICI for Gasoline Direct-Injection Compression Ignition) in the low temperature combustion (LTC) regime is presented. As an aid to plan engine experiments at full load (16 bar IMEP, 2500 rev/min), exploration of operating conditions was first performed numerically employing a multi-dimensional CFD code, KIVA-ERC-Chemkin, that features improved sub-models and the Chemkin library. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion. Operation ranges of a light-duty diesel engine operating with GDICI combustion with constraints of combustion efficiency, noise level (pressure rise rate) and emissions were identified as functions of injection timings, exhaust gas recirculation rate and the fuel split ratio of double-pulse injections.