Experiments have been carried out on a dynamic combustion rig in order to study the ignition and early phase of combustion of liquefied Volatile Organic Compounds (named VOC Fuel). The VOC was ignited by pilot diesel in a CI process. Two separate nozzles have been employed for the VOC and pilot fuel, respectively. Schlieren images were taken of the early combustion phase, together with recordings of the most important process parameters.
The main aim of the study was to investigate whether the use of VOC Fuel would give any deviations compared to normal diesel fuel operation. Combustion characteristics of VOC Fuels were studied in separate test series, both for single VOC components and for mixtures of VOC.
Several test parameters were varied during the experiments with pilot diesel ignition of VOC Fuel. These variables were the following:
Combustion of typical VOC Fuel components is shown to be faster than diesel once it is ignited. The ignition delay decreases as the length of the injected fuel molecule increases. All the VOC Fuel components studied have a longer ignition delay than diesel fuel, in addition to being more unstable. Engine operational problems are therefore likely to arise if injecting only VOC Fuel. Among the fuels tested propane is the most problematic component, while n-butane gives the most stable ignition.
The tests using pilot ignition showed that the shortest ignition delay period was found when injecting the pilot fuel and VOC Fuel simultaneously.
The results from the experiments show that as long as the VOC Fuel is ignited by pilot fuel, stable ignition is obtained.