Process for Study of Micro-pilot Diesel-NG Dual Fuel Combustion in a Constant Volume Combustion Vessel Utilizing the Premixed Pre-burn Procedure

A constant volume spray and combustion vessel utilizing the pre-burn mixture procedure to generate pressure, temperature, and composition characteristic of near top dead center (TDC) conditions in compression ignition (CI) engines was modified with post pre-burn gas induction to incorporate premixed methane gas prior to diesel injection to simulate processes in dual fuel engines. Two variants of the methane induction system were developed and studied. The first used a high-flow modified direct injection injector and the second utilized auxiliary ports in the vessel that are used for normal intake and exhaust events. Flow, mixing, and limitations of the induction systems were studied. As a result of this study, the high-flow modified direct injection injector was selected because of its controlled actuation and rapid closure.

Further studies of the induction system post pre-burn were conducted to determine the temperature limit of the methane auto-ignition. It was found that for sufficient induction and mixing time determined from experimental observations and CFD modeling studies, a maximum core temperature of 750 K at the time of micro-pilot diesel injection can be achieved. Although lower than TDC temperatures in diesel CI engines, this temperature is sufficient for studying dual fuel injection and auto-ignition with high cetane fuels. Results from this work confirm the feasibility of dual fuel combustion using the proposed CV process and provide constraints for further micro-pilot diesel-NG dual fuel combustion studies.