Investigation of the cold-start combustion characteristics of ethanol-gasoline blends in a constant-volume chamber

This experimental study conducted in a closed combustion chamber is to investigate combustion characteristics of ethanol-gasoline blends at low temperature, which is related to the cold-start operation of engines fueled with ethanol-gasoline. It presents the effects of the fuel amount injected into the combustion vessel on the combustion process, and some key characteristic parameters, such as ignition delay time, mass burning rate, and flame speeds, have been explored. The result shows that, for an ethanol-gasoline engine, it must not be overfueled to realize a reliable cold start, as is the case for a gasoline engine at the same temperature, especially at a temperature range around ethanol's boiling point, because ethanol addition into gasoline results in the improvement of blend evaporation. Moreover, The exhaust emissions are purposely measured in terms of unburned hydrocarbon (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) emissions. It is confirmed that the emissions of HC during rich combustion at relative low temperature should be increased with the increasing addition of ethanol into gasoline, but at separated optimization equivalence ratio for cold start, HC and CO emissions can be obviously reduced. The flame speeds are investigated as well. It is shown that, for ethanol-gasoline blends with ethanol content below 30%, the suitable fuel-air ratio to realize fast flame propagation is about 1.3.