Abstract
Key words
MPI spark-ignited gas-fuelled engine, alternative fuels, compressed natural gas, emission control
Abstract
The demand for improving engine emissions, performance and efficiency requires the application of advanced identification and control strategies [2, 8]. The most promising methods of improving the engine emission performance are: combustion optimisation, use of alternative fuels and after-treatment technologies. The main objective of this research work was to optimise the multi-point CNG fuel injection system of the newly converted spark-ignited bi-fuel engine VW 1.4L 16V AUA such that it would meet the Euro 4 emission limits. Emission tests and measurements were carried out on the engine dynamometer SCHENCK WS-230. The experimental setup consists of multi-port CNG fuel injection system DREAM XXI, developed by OMVL of Italy, with close-loop emission control technology. The air-excess ratio and the emissions were monitored over a range of speeds (1500 to 5350 min-1) and loads (25, 40, 60 and 100%) of the newly integrated MPI for CNG. At each operating condition the injection time map of ECU was tuned to achieve optimum emissions under CNG operation. The value of maximum engine power with Nat95 petrol fuel at 5000 rpm was 53 kW while the power generated with CNG fuel at the same rpm was 43.8 kW; that means 17% power loss with unchanged compression ratio and ignition advance angle. The results of emission measurements on CNG fuel give positive provision to fulfil the Euro 4 emission standard. The CO and CHx values are very low (often zero) on both fuels. Compared to gasoline, higher value of NOx was registered in CNG fuel operation (especially on partial load), approximately in the range of up to 100 ppm. The CO2 emissions in CNG fuel operation are about 20-25% lower than in petrol operation.