Theoretical and Experimental Validation of Engine Performance and Combustion Characteristics in a Spark Ignition Engine

The objective of the study was to validate by experimentation theoretical parameters of performance and combustion characteristics obtained using kiva4. Engine performance is critical in understanding the operation of an internal combustion engine. It is usually represented by characteristic curves or characteristic profiles which are a function of engine parameters. Experiments and measurements were performed in an engine test room in the department of Electrical Engineering at The Copperbelt University in Kitwe Zambia. The engine on which tests were conducted was mounted on a test bench and it was fitted with an air-cooled eddy current dynamometer which was able to provide a maximum raw torque of 34 N-m with a precision of ± 0.5%. Test data to validate kiva4 simulation results were conducted on a 3-cylinder, four-stroke Volkswagen (VW) Polo 6 TSI 1.2 gasoline engine. In one set, variations in exhaust gas temperature were studied by varying the engine load, while keeping the engine speed constant. In another test, exhaust gas temperature variations were studied by keeping the engine at no load whilst varying the speeds. A third experiment examined fluctuations in exhaust gas temperature while the engine was operating under a constant load and different engine speeds. An itape17 file with a 450 asymmetrical mesh was produced using the simple grid/mesh generator K3PREP in order to analyse fluctuations in exhaust gas temperatures under test settings. Simulations were therefore performed based on the input parameters established in the conducted tests. Results showed that, in the first test, power increased with load while specific fuel consumption reduced and brake thermal efficiency improved. In the second test, exhaust gas temperatures ranged from 510K to 685K while simulations with the Kiva4 code showed exhaust gas temperatures of 507K and 667K at 850rpm and 2500rpm, respectively. In the third test experimental results for the exhaust gas temperatures were 474K to 575K compared with Kiva4 results, of 507K to 667K at 2000rpm and 2500rpm, respectively. Simulations with the kiva4 code showed a significant predictability of the performance characteristics of the engine. This was evident in the appreciable agreement obtained in the simulation results when compared with the test data, under the considered test conditions. The exhaust gas temperature fluctuates depending on the engine load and speed as the exhaust gas temperature increases with increasing speed and load. There are also temperature pulsations, caused by the character and arrangement of the internal combustion engine, where the individual chambers ignite gradually, and the corresponding temperature pulsations occur in the exhaust pipe. A percentage error, between experimental results and results from simulations with the kiva4 code of only between 2% to 3% was observed.