Research and development toward an ethanol-natural gas bi-fuel spark-ignited engine

Abstract

A large brewery can generate approximately 480,000 gallons of waste 200 proof ethanol annually. At the time of writing, Caterpillar Inc. does not offer an engine capable of using ethanol as fuel. This thesis presents the development of a bi-fueled engine capable of operating on ethanol or NG. The study focuses on three primary components: a techno-economic analysis of a Fort Collins, CO brewery producing waste ethanol; the design, build, and integration of an ethanol capable fuel system onto a Cat® CG137-8; and development of a GT-Power model of the Cat CG137-8 with ethanol capabilities. The techno-economic analysis evaluates engine size, configuration, operating strategy, and number of units deployed. It emphasizes the value of free fuel and the importance of maximizing the energy captured from it. The fastest break-even time and highest five-year NPV is achieved using a single Cat G3412C (500 kW) engine operating solely on ethanol in a CHP configuration for approximately 7500 hr/year. This configuration yields a five-year NPV of $75,000 and a break-even time of 4.3 years. Experimental efforts involve designing, building, and integrating an ethanol capable fuel system on a Cat CG137-8 engine for bi-fuel operation. The process includes selecting and testing fuel system components, designing injector bosses and cylinder head modifications, disassembling and reassembling the engine, and integrating the hardware with the Cat CG137-8 engine control module and LabVIEW data acquisition system. Commissioning reveals that the fuel rail pressure varies with engine load, ethanol requires less intake manifold pressure than NG, and the maximum brake torque timing at rated speed and 25% load corresponds to a CA50 of approximately 11° after top dead center. A NG GT-Power model of the Cat CG137-8 provided by Caterpillar Inc. is retrofitted with ethanol capabilities to validate experimental data, assess fuel system limitations, and compare ethanol to NG. The retrofitted model is tuned using experimental data to match brake efficiency, fuel flow, temperatures, and pressures. Once tuned, a maximum brake torque test is performed, reveling at 100% load a CA50 of approximately 3.5° after top dead center produces the highest brake efficiency. Comparisons between NG and ethanol show that ethanol exhibits a lower intake manifold temperature, which reduces the required intake manifold pressure to produce the same power. Maximum power simulations indicate that, at 5000 ft elevation, ethanol has the potential to produce 415.8 kW.