Development of fuel flexible engine control system

Biomass resources are drawing attention as alternative fuel for combating the energy crisis and for atmospheric environment protection. The small gas engine in a distributed power generation system is an efficient system to use it, because the biomass resource is stored in large area and its energy density is low. The composition of gas fuel generated from biomass is affected by the source type, the gasification method, and the gasifying condition. Then, the gas engine must be operated stably with high thermal efficiency in view of these fuel fluctuations. The authors aim to develop a small gas engine system for biomass gas by modifying the control system of a conventional spark ignition engine to absorb fuel fluctuation. Then, the original gas engine control algorithm was developed, which can define target values of equivalence ratio of premixture and ignition timing realizing high thermal efficiency in fuel combustion property by analyzing in-cylinder pressure data in real time. To develop a control algorithm, combustion experiments with various components fuels assuming component of real biomass gases like as fermentation gas and pyrolysis gas, were carried out. It was clarified that the relationship between dimensionless combustion duration and equivalence ratio is expressed in first order liner function regardless of fuel components. Indicated thermal efficiency can be also expressed by dimensionless combustion duration and volumetric efficiency. In addition, the relationship between combustion duration and MBT can also be expressed in first order function regardless of fuel components. Original engine control algorithm uses these relationships obtained from in-cylinder gas pressure in real time. Thus, biomass fueled gas engine system was developed by applying the algorithm to the automobile gasoline engine with hardware modifications of only fuel supply system and flywheel. The engine system was connected to a gasification plant using wood chip and operation test was carried out. As a result, the engine system could set optimum premixture condition and ignition timing, which realized stable and high thermal efficiency operation automatically.