LNG injection into engine combustion chamber for combined cycle

Abstract

The article presents theoretical and experimental studies to justify the possibility of controlling supply of liquefied natural gas (LNG) to the engine cylinder. At present, most gas engines have operating cycle with constant volume combustion (N. Otto cycle). This is due to difficulty of supplying natural gas in top dead center region. N. Otto cycle significantly loses in efficiency to combined cycle with combustion at constant volume and constant pressure (G. Trinkler cycle). The experiment was carried out on marine diesel engine “NVD-24” stand on a mixture of diesel fuel and petroleum gas in various proportions, at idle and with partial engine load. It has been established that liquefied petroleum gas under pressure is mixed with diesel fuel in any proportions, while mixture remains a homogeneous liquid, without visible precipitation and stratifycation. Calculations of theoretical cycles have been performed, showing the advantages of the injection of a combustible mixture at the top dead center, in comparison with preliminary carburetion. During the experiment, it was found that an engine with a spool injection pump and a spring nozzle, can operate stably using a liquid mixture as a fuel without adding additives. An increase in the effective efficiency of the engine with an increase in the concentration of LNG in the supplied fuel mixture has been established. In this case, fuel mixture pressure must be greater than critical pressure of the gas mixture. Formulas for calculating advance angle of fuel supply to the top dead center and angle of delivery behind the top dead center are obtained. The performed calculations in relation to “NVD-24” engine show that Common Rail fuel supply system with a piezoceramic injector can ensure the operation of the engine in a combined cycle. This organization of workflow makes it easy to upgrade both new engines and those in operation. In this case, fuel supply can be performed on all engines, regardless of presence of gas turbine pressurization.