Emissions from an extreme-compression, free-piston engine with diesel-style combustion

Abstract

As part of an ongoing effort to demonstrate operation of a free-piston internal combustion engine at extremely high compression ratios, this paper reports the measurement of emissions from diesel-style combustion of a single-cycle, free-piston research device capable of achieving compression ratios up to 100:1. The ability to measure gaseous and particulate emissions was added to the existing extreme-compression device. These systems and their characterization are described. Concentrations as well as specific emissions are reported for carbon monoxide, total oxides of nitrogen, unburned hydrocarbons, carbon dioxide, oxygen, and soot. A first set of emissions data is reported of a pure-component fuel (isooctane) at a moderate compression ratio (∼35:1) over a range of equivalence ratios, in order to characterize the emission measurement system as well as diesel-style combustion in the free-piston device. NOx emissions were essentially constant over the range of equivalence ratios. CO, HC, and soot emissions were low at the lowest equivalence ratio, and increased dramatically for equivalence ratios greater than ∼0.6. A second set of results is reported consisting of diesel combustion at ∼0.5 equivalence ratio, for compression ratios up to 100:1. CO, HC, and soot emissions remained low over the range of compression ratios, resulting in high combustion efficiency, even at 100:1 compression ratio. NOx emissions increased by a factor of 5 from 35:1 to 100:1 compression ratio, likely due to the far higher combustion temperatures.