| Summary: | At the moment the main impetus to move towards alternative fuels produced from renewable resources is legislation and market forces, which push the automotive industry to limit pollutant emissions. One way of reducing these hannful emissions is to replace the conventional fossil fuel totally with syngas or partially with alcohols and/or their ethers. The bending of alcohols to gasoline has been attempted since the mid of 1970's and recently it is in practice in some countries. Interestingly, alcohols are more competitive among the other alternatives such as syngas because they are compatible with existing fuelling distribution infrastructure and are easily stored in a vehicle. However, this blending may change the burning rate which consequently changes the level of cyclic variations. Cycle-to-cycle variability is the main cause of reduction in power output and efficiency and deterioration in the vehicle driveabiIity. Therefore, the main objective of this study was to investigate the impact of employing renewable fuels in spark ignition engine on the cycle-to-cycle variations. The employed fuels involved synthetic gas mixture of 2H2+CO, blends of Ethyl Tert Butyl Ether (ETBE) with primary reference fuel (PRF), and a commercial gasoline fuel (EOS) containing 5 % by volume of ethanol. In the first stage of this work, Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) techniques were employed to characterise the in-cylinder turbulent flow at different engine speed during motoring cycles. In the main stage of the current study, PlY and LDV was also employed to monitor the in-cylinder flow during firing experiments simultaneously with natural light video photography for recording the flame propagation and pressure recordings methods. Results verified that, there was a slight increase in the cyclic variability of the indicated mean effective pressure with increasing the percentage of ETBE in the mixture. The cyclic variability has decreased when using E05 in comparison with PRF or its blends with ETBE. On the other hand, it was possible to run the engine at an equivalence ratio of 0.3 with 2H2+CO due to the extended flammability limit of hydrogen containing mixtures. Spatial and temporal analysis of flow field parameters for individual cycles was adopted in the current study. The analysis showed that there is a high degree of connection between early flame kernel development, RMS turbulent velocity and global burning rate of a cycle, such that a cycle that start fast will remain fast throughout the cycle in most cases.
|
|---|
