Mechanical Engineering - Theses
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ItemReducing cold start fuel consumption through improved thermal management( 2008)The thesis presents research in achieving faster warm-up of an SI engine, thereby affecting the fuel economy penalty. The faster warm-up relates to faster heating of the cylinder head and engine block, targeting reducing viscous friction in the cold oil as the most likely candidate to improve. The strategy applied was to reduce the coolant flow circulation rate to achieve a faster warm-up of the engine. A lumped parameter model for engine heat transfer, coolant flow and heat capacities, in a single cylinder, based on engine operating points like spark advance, engine speed and MAP was built in Modelica. The engine used for experimentation was a Ford in-line, 4 stroke, 6-cylinder engine, with a compression ratio of 10.3:1, in which 56 K-type thermocouples were installed at different locations to measure the temperature. The experiments were performed with varying coolant flow rate from normal down to zero, utilizing an electric water pump, over an approximation to the New European Drive Cycle (NEDC), at a speed of 1161 rev/min and load of 48 Nm. The selected speed and load were the average operating condition for 180 seconds of engine running over the urban part of a simulated NEDC. In addition, the coolant circuit was modified to a split cooling supply and the sets of results analyzed to find the reduction in engine warm-up time and fuel consumption. It is shown from the results that the warm-up time of the engine and the fuel consumption were notably reduced, as the flow was reduced from maximum to minimum in steps. On average over an interval of engine running for 300 seconds from cold start, the cylinder head temperature was increased by about 2°C , the average engine block temperature was increased by about 6.5°C and the average cylinder head coolant temperature was increased by about 4°C . However, the bulk temperature of the oil in the oil sump showed marginal improvement and remained consistent, even at the lowest coolant flow rate. Nonetheless, the improvements in block temperature had significant effects on reducing the friction between the piston and cylinder walls. Analysis of the results show that the coolant flow pattern changed with the use of an electric water pump. The flow is less evenly distributed around the cylinders with the use of an electric water pump, whilst retaining the mechanical water pump body, compared to the mechanical water pump operation. The model was applied to simulate for two engine operating points, i.e., 1161 rev/min, 48 Nm load and 700 rev/min and 0 Nm load. The model was calibrated at 1161 rev/min, 48 Nm load and validated at 700 rev/min, 0 Nm load. The modeling results were in fair agreement with the experimental results. The model can be employed to investigate electric water pump control. The important finding is that around 3% fuel consumption savings are possible over the NEDC by management strategies that lead to faster cylinder block warm up, even though this may result in little or no change in oil temperature as measured in the sump.