Part 2. Conceptual Design of Efficient Spark Ignition Engines Using Biogas and Natural Gas

This paper presents a conceptual design for efficient spark ignition (SI) engines using biogas and natural gas, it is based on the thermodynamics laws, and three scientific methodologies. 1. Methane number (MN) measure, 2. Energy quality estimation for gaseous fuels, 3. Exergy estimation for SI engines is limited by the knocking phenomenon. Own experimental data from two engines are used. 1. A cooperative fuel research engine (CFR) to measure the fuel's critical compression ratio (CCR) and MN, using fuels with MN ranging from 37–140. 2. A hybrid diesel engine converted to biogas SI (BSI) operation, with high CR, using custom pistons (designed by CFD simulations) to rise turbulence intensity for biogas combustion. The diesel engine used for the conceptual design is 4 cylinders, with a displacement of 4 liters, and a CR of 17.5:1 with a maximum output power of 38 kW and thermal efficiency of 31.35%. It is presented a review of the literature related to the concepts of availability and exergy for fuels in internal combustion engines (ICE). Correlations between MN and research octane number (RON) are used to develop the conceptual design. It is proposed a correlation between the fuel's exergy, entropy, and octane.