An optical investigation of combustion process of a direct high-pressure injection of natural gas

Abstract

More than 90% of worldwide cargo transportation is carried out by ships. Nowadays, a contradictory circumstance like tough exhaust emission regulations for ocean-going ships by International Maritime Organization (IMO) and deterioration in the quality of marine fuel forces some challenges. A change to another fuel, such as liquefied natural gas (LNG), is conceivable. To create ideas for such the new combustion system, it is essential to visualize the combustion process and find the actual problems. For that target, a world largest class Rapid Compression and Expansion Machine (RCEM with 200-mm-wide or 240-mm-diameter window) that holds under 20 MPa cylinder pressure has been designed and built by the authors. This RCEM is equipped with several electronically controlled fuel injection systems for both liquid fuel and gas fuel. Characteristics of diesel spray combustion and gas injection (GI) combustion can be analyzed using direct photography and some kinds of laser optical techniques. After one-shot burning of the fuel, the burnt gas is sent from RCEM to a gas analyzer and NOx, CO, CO2 and THC can be measured. In this paper, a fundamental difference of combustion process between diesel and GI is made clear. However, as GI combustion emits much higher NOx than the lean-burn, some measures like EGR is necessary for the IMO Tier 3 NOx regulation. The GI combustion under EGR atmosphere (lower oxygen %) is also visualized. Some data of GI combustion are obtained by above-mentioned experiments. However, the phenomena are too complicated. As the next task, to create and validate a calculation model is important to optimize the GI system. In this study, the three-dimensional CFD code, KIVA3V, combined with the software tool for solving complex chemical kinetics, SENKIN, was modified for GI combustion.