Search Results

The effects of fuel composition on homogeneous charge compression ignition (HCCI) combustion were studied experimentally in an engine employing negative valve overlap (NVO). Three test fuels, varying in ignition quality and volatility, were investigated for their effect on engine performance and combustion phasing; comparisons were made to a full-run 87-octane base fuel. The three test fuels, which varied in research octane number from 69 to 98, were all found to advance the combustion timing slightly relative to the base fuel, suggesting some differences in the ignition chemistry. The combustion performance at a fixed combustion phasing, however, was found to be comparable, within the limits of the system, for all of the fuels. A major testing issue that limited the system repeatability was the formation of combustion chamber deposits under some operating conditions. A methodology to mitigate these effects was employed with some success.

The KIVA 3V code has been applied to predict combustion chamber heat flux in an air-cooled utility engine. The KIVA heat flux predictions were compared with experimentally measured data in the same engine over a wide range of operating conditions. The measured data were found to be approximately two times larger than the predicted results, which is attributed to the omission of chemical heat release in the near-wall region for the heat transfer model applied. Modifying the model with a simple scaling factor provided a good comparison with the measured data for the full range of engine load, heat flux sensor location, air-fuel ratio and spark timings tested. The detailed spatially resolved results of the KIVA predictions were then used to develop a simplified model of the combustion chamber temporally integrated heat flux using an artificial neural network (ANN).

Planar laser-induced fluorescence of 3-pentanone doped into the fuel (iso-octane) and OH, which is present in the combustion products, was performed in an optically accessible direct-injection spark-ignition (DISI) engine under stratified and homogeneous operating conditions. A wall-guided, swirl-based combustion chamber was utilized, and experiments were performed for light load, where the fuel-air equivalence ratio was 0.3, and high load conditions, with an equivalence ratio of 0.7, at speeds of 600 and 1200 rpm. The 3-pentanone images were calibrated through the use of a premixed charge condition of known equivalence ratio, with corrections applied for number density changes due to combustion. At the light load condition combustion of the highly stratified fuel cloud was directly measured for the first time. The equivalence ratio of the mixture at the flame front was found to be in the range from 0.5 - 0.8 for optimized combustion conditions in this engine.

In-cylinder thermal barrier coatings (TBCs) have the capability to reduce fuel consumption by reducing wall heat transfer and to increase exhaust enthalpy. Low thermal conductivity, low volumetric heat capacity thermal barrier coatings tend to reduce the gas-wall temperature difference, the driving potential for heat transfer from the gas to the combustion chamber surfaces. This paper presents a coupling between an analytical methodology for multi-layer coated wall surface temperature prediction with a fully calibrated production model in a commercial system-level simulation software package (GT-Power). The wall surface temperature at each time step was calculated efficiently by convolving the engine wall response function with the time-varying surface boundary condition, i. e., in-cylinder heat flux and coolant temperature. This tool allows the wall to be treated either as spatially uniform with one set of properties, or with independent head/piston/liner components.

Thermal swing coatings that have low volumetric heat capacity and low thermal conductivity are attractive because they have the potential to significantly reduce heat transfer to the combustion chamber walls. This paper presents an analytical method for determining the exact solution of the time-resolved wall temperature during the engine cycle for any number of coating layers and properties using the Laplace transformed heat diffusion equation. The method relies only on material properties and the past heat flux history, and represents the exact solution of the heat diffusion equation. The analytical nature of the solution enables fast computation and, therefore, application to system-level optimization calculations. The model relies on an assumption of one-dimensional heat flow, and constant material properties.