Development of Flexible Gas Fuel Engine System

Abstract

In this study, the authors aim to develop a small gas engine system for biomass gas by modifying the control system of a conventional spark ignition engine. Before developing a control algorithm, combustion experiments with various component fuels assumed to have the components of real biomass gases, such as fermentation and pyrolysis gases, were carried out. It was clarified that the relationship between dimensionless combustion duration and equivalence ratio can be expressed by a first-order linear function regardless of fuel composition. Indicated thermal efficiency can also be expressed by combustion duration and volumetric efficiency when the coefficient of variation of indicated mean effective pressure is lower than 5% and pumping loss decreases against volumetric efficiency linearly, and the relationship between combustion duration and MBT can also be expressed by a first-order function. By using these relationships, a gas engine control algorithm, which can define the target values of the equivalence ratio of a premixture and ignition timing that realize a high thermal efficiency for fuel compositions automatically by analyzing in-cylinder gas pressure data in real time, is developed in order to use gaseous fuels produced from biomass resources effectively. Thus, a biomass gas fuel engine system is developed by applying the algorithm to an automobile gasoline engine, hardware modifications of which are only the fuel supply system and flywheel. The engine system is connected to a gasification plant using wood chips and an operation test is carried out. As a result, the engine system can set an optimum premixture condition and an ignition timing, which realizes a stable and high-thermal-efficiency operation automatically.