Availability Analysis of Alternative Fuels for Compression Ignition Engine Combustion

Modeling of engine heat release from in-cylinder pressure is a common practice for characterizing engine combustion. Fuel property variation induces changes in engine performance, which can be categorized through heat release modeling. One under-utilized form includes an availability analysis that links changes in fuel properties to the amount of availability extracted as work or lost through inefficiencies. Here, a diagnostic heat release model is used to catalogue both the 1st and 2nd Law behavior of numerous alternative fuels. Conventional engine combustion using diesel, biodiesel, renewable jet fuel, and waste-plastic derived diesel are studied, alongside dual-fuel operation of compressed natural gas (with diesel) and synthesis gas (with biodiesel), allowing for the exploration of combustion with respect to changing fuel properties. In particular, more ideal fuel mixing is generally reflected directly in the 2nd Law efficiency. However, high viscosities largely result in a later availability addition that is not extracted as work. While this availability would be wasted at exhaust blowdown, deliberately increasing later temperatures may be useful if paired with exhaust heat recovery systems. Overall, the 2nd Law model presents these tradeoffs more clearly than a traditional 1st Law analysis; thus, its further use may be warranted in concert with advanced engine combustion modes.