Effect of materials on the autoignition of cyclopentane

Cyclopentane, a flammable hydrocarbon, is being considered as a working fluid for waste heat recovery applications using Organic Rankine Cycles with Direct Evaporators. A postulated failure mode consisting of a pinhole leak in a heat exchanger tube raises safety concerns due to autoignition of the working fluid. Experiments were conducted to determine the ignition delay time (IDT) of cyclopentane using an Ignition Quality Test™ (IQT™) device. Two sets of experiments were conducted per ASTM D6890 (with exception to charge pressure and temperature) to determine ignition delay of the fuel at atmospheric pressure for standard air (∼20.95% oxygen) and vitiated air (13.3% oxygen) at a temperature of 803 K. Operation of the IQT device at a much lower pressure (1 bar) than normal operation (21.4 bar) with a standard injector led to very rich conditions and wetting of the stainless steel chamber walls. Catalytic effects are postulated to produce the small IDTs observed. Experiments were repeated with a modified injector to prevent wall wetting, resulting in average IDTs that are substantially longer.