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This paper presents engine dynamometer testing and modeling analysis of ethanol compared to gasoline at part load conditions where the engine was not knock-limited with either fuel. The purpose of this work was to confirm the efficiency improvement for ethanol reported in published papers, and to quantify the components of the improvement. Testing comparing E85 to E0 gasoline was conducted in an alternating back-to-back manner with multiple data points for each fuel to establish high confidence in the measured results. Approximately 4% relative improvement in brake thermal efficiency (BTE) was measured at three speed-load points. Effects on BTE due to pumping work and emissions were quantified based on the measured engine data, and accounted for only a small portion of the difference.

One of the characteristics of nominally homogeneous charge spark ignition engines is a pronounced variation in the combustion rate from cycle to cycle. Many theories have been advanced which attempt to explain the fundamental origin for differences on a cyclic basis. In the present work, some of the suspected causes or their manifestations have been incorporated into Ford's engine combustion model with the intention of determining if their impact on the combustion rate is as theorized. It has been found that initial spark kernel burn rate, the displacement of the spark kernel from the spark plug gap, and the turbulence intensity must all be perturbed simultaneously on a cycle-by-cycle basis to cause the cycle simulation program to mimic the experimentally determined burn parameters with respect to their averages and distributions.

Tumble flow has been recognized as an important and positive enhancement of combustion for SI engines. Tumble flow modeling with quasi-dimensional models is difficult because of the transient nature of tumble vortex, compared with swirl flows. Although multi-dimensional models have obtained plenty of attention recently in engine research, quasi-dimensional SI engine models will continue to dominate industrial applications in the near future. In the present research, a bulk flow model has been developed for tumble flows based on angular momentum conservation. Its effect on turbulence was then modeled using a Two-Equation Model (k-ε Model). A methodology has also been developed to use particle tracking velocimetry (PTV) measurement to calibrate the quasi-dimensional bulk flow model at engine BDC to model tumble vortex and tumble-generated turbulence. The Entrainment Combustion Model was used for combustion modeling.