Search Results

The exhaust emission and performance characteristics of a 100% biodiesel fuel was evaluated on a single cylinder direct injection diesel engine that had been modified to allow multi-pulse diesel fuel injection at the intake port and independent control of intake heating, exhaust gas recirculation and throttling. Firstly, conventional single-shot direct injection tests were conducted and comparisons made between the use of an ultra-low sulphur diesel fuel and the biodiesel fuel. Secondly, tests for the premixed combustion of neat biodiesel were performed. Exhaust gas recirculation was applied extensively to initiate the low temperature combustion for the conventional in-cylinder single injection operation and to moderate the timing of the homogeneous charge compression ignition for the intake-port sequential injection. Because of the high viscosity and low volatility of the biodiesel, pilot-ignited homogeneous charge compression ignition was used.

The effects of turbulence on 60% stoichiometric, premixed methane-air flame propagation were investigated using high speed schlieren video and pressure trace analyses. The mixtures were centrally spark-ignited at 300 K and 101 kPa in a 125 mm cubical chamber. Turbulence was up to 2 m/s intensity with 2 to 8 mm integral scale. With quiescent mixtures, buoyancy convected the slow-burning flame upward onto the upper wall, resulting in dramatic heat loss. With turbulence, the burning rate was enhanced profoundly, though partial flame quenching resulted in cyclic variability at higher turbulence levels. Despite this partial quenching, these ultra-lean flames generally resisted total extinguishment over the conditions tested.

The different roles played by small and large eddies in engine combustion were studied. Experiments compared natural gas combustion in a converted, single cylinder Volvo TD 102 engine and in a 125 mm cubical cell. Turbulence is used to enhance flame growth, ideally giving better efficiency and reduced cyclic variation. Both engine and test cell results showed that flame growth rate correlated best with the level of high frequency, small eddy turbulence. The more effective, small eddy turbulence also tended to lower cyclic variations. Large scales and bulk flows convected the flame relative to cool surfaces and were most important to the initial flame kernel.