Search Results

An analysis method for characterizing fuel behavior during spark-ignition engine starting has been developed and applied to several sets of start-up data. The data sets were acquired from modern production vehicles during room temperature engine start-up. Two different engines, two control schemes, and two engine temperatures (cold and hot) were investigated. A cycle-by-cycle mass balance for the fuel was used to compare the amount of fuel injected with the amount burned or exhausted as unburned hydrocarbons. The difference was measured as “fuel unaccounted for”. The calculation for the amount of fuel burned used an energy release analysis of the cylinder pressure data. The results include an overview of starting behavior and a fuel accounting for each data set Overall, starting occurred quickly with combustion quality, manifold pressure, and engine speed beginning to stabilize by the seventh cycle, on average.

The purpose of this work was to develop an understanding of how liquid fuel transported into the cylinder of a port-fuel-injected gasoline-fueled SI engine contributes to hydrocarbon (HC) emissions. To simulate the liquid fuel flow from the valve seat region into the cylinder, a specially designed fuel probe was developed and used to inject controlled amounts of liquid fuel onto the port wall close to the valve seat. By operating the engine on pre-vaporized Indolene, and injecting a small amount of liquid fuel close to the valve seat while the intake valve was open, we examined the effects of liquid fuel entering the cylinder at different circumferential locations around the valve seat. Similar experiments were also carried out with closed valve injection of liquid fuel at the valve seat to assess the effects of residual blowback, and of evaporation from the intake valve and port surfaces.

A single-zone burn-rate analysis based on measured cylinder pressure data proposed by Gatowski et al. in 1984 was evaluated over the full load and speed range of a spark-ignition engine. The analysis, which determines the fuel mass burning rate based on the First Law of Thermodynamics, includes sub-models for the effects of residual fraction, heat transfer, and crevices. Each of these sub-models was assessed and calibrated. Cylinder pressure data over the full engine operating range obtained from two different engines were used to examine the robustness of the analysis. The sensitivity of predictions to the parameters wall temperature, heat transfer model coefficients and exponent, swirl ratio, motoring polytropic constant, in-cylinder mass, and to uncertainty in pressure data was evaluated.

The influence of charge motion and fuel injection characteristics on diesel combustion was studied in a rapid compression machine (RCM), a research apparatus that simulates the direct-injection diesel in-cylinder environment. An experimental data base was generated in which inlet air flow conditions (temperature, velocity, swirl level) and fuel injection pressure were independently varied. High-speed movies using both direct and shadowgraph photography were taken at selected operating conditions. Cylinder pressure data were analyzed using a one-zone heat release model to calculate ignition delay times, premixed and diffusion burning rates, and cumulative heat release profiles. The photographic analysis provided data on the liquid and vapor penetration rates, fuel-air mixing, ignition characteristics, and flame spreading rates.

The in-cylinder hydrocarbon (HC) mole fraction was measured on a cycle-resolved basis during simulated starting and warm-up of a port-injected single-cylinder SI research engine on a dynamometer. The measurements were made with a fast-response flame ionization detector with a heated sample line. The primary parameters that influence how rapidly a combustible mixture builds up in the cylinder are the inlet pressure and the amount of fuel injected; engine speed and fuel injection schedule have smaller effects. When a significant amount of liquid fuel is present at the intake port in the starting process, the first substantial firing cycle is often preceded by a cycle with abnormally high in-cylinder HC and low compression pressure. An energy balance analysis suggests that a large amount of liquid vaporization occurs within the cylinder in this cycle.

1 Downsizing and turbocharging a spark-ignited engine is becoming an important strategy in the engine industry for improving the efficiency of gasoline engines. Through boosting the air flow, the torque is increased, the engine can thus be downsized, engine friction is reduced in both absolute and relative terms, and engine efficiency is increased. However knock onset with a given octane rating fuel limits both compression ratio and boost levels. This paper explores the operating limits of a turbocharged engine, with various gasoline-ethanol blends, and the interaction between compression ratio, boost levels, and spark retard, to achieve significant increases in maximum engine mean effective pressure and efficiency.

Photographic and performance studies with a Rapid Compression Machine at the Massachusetts Institute of Technology have been used to develop insight into the role of mixing in diesel engine combustion. Combustion photographs and performance data were analyzed. The experiments simulate a single fuel spray in an open chamber diesel engine with direct injection. The effects of droplet formation and evaporation on mixing are examined. It is concluded that mixing is controlled by the rate of entrainment of air by the fuel spray rather than the dynamics of single droplets. Experimental data on the geometry of a jet in a quiescent combustion chamber were compared with a two-phase jet model; a jet model based on empirical turbulent entrainment coefficients was developed to predict the motion of a fuel jet in a combustion chamber with swirl. Good agreement between theory and experiment was obtained.

A gasoline direct injection fuel spray was observed using a fired, optical access, square cross-section single cylinder research engine and high-speed video imaging. Spray interaction with the piston is described qualitatively, and the results are compared with Computational Fluid Dynamics (CFD) simulation results using KIVA-3V version 2. CFD simulations predicted that within the operating window for stratified charge operation, between 1% and 4% of the injected fuel would remain on the piston as a liquid film, dependent primarily on piston temperature. The experimental results support the CFD simulations qualitatively, but the amount of fuel film remaining on the piston appears to be under-predicted. High-speed video footage shows a vigorous spray impingement on the piston crown, resulting in vapor production.