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Design considerations for an engine-integrated reciprocating natural gas compressor




Malakoutirad, Mohammad, author
Bradley, Thomas H., advisor
Young, Peter, committee member
Olsen, Daniel, committee member

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This thesis presents the development of an engine retrofit concept to turn a ICE vehicle's engine into a compressor for convenient natural gas refueling, as opposed to building a smaller secondary standalone unit. More specifically, this project seeks to outfit an internal combustion engine (ICE) to serve the dual purposes of providing vehicle propulsion and compression for natural gas refueling with minimal hardware substitution. The principal objective of this thesis is to describe and analyze the dynamic and thermal design considerations for an automotive engine-integrated reciprocating natural gas (NG) compressor. The purpose of this compressor is to pressurize storage tanks in NG vehicles from a low-pressure NG source by using one of the cylinders in an engine as the compressor. The engine-integrated compressor is developed by making minor changes to a 5.9 liter displacement diesel-cycle automotive engine. In this design, a small tank and its requisite valving are added to the engine as an intermediate storage tank to enable a single compressor cylinder to perform two-stage compression. The resulting pressure in the compressor cylinder and storage tank is 25 MPa, equivalent to the storage and delivery pressure of conventional compressed NG delivery systems. The dynamic simulation results show that the high cylinder pressures required for the compression process create reaction torques on the crankshaft, but do not generate abnormal rotational speed oscillations. The thermal simulation results show that the temperature of the storage tank and engine increases over the safety temperature of the NG unless an active thermal management system is developed to cool the NG before it is admitted to the storage tanks. Results are then translated into vehicle-level operating costs and petroleum consumption for a dual-fuel NG-diesel vehicle.


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