Abstract
High-speed imaging of fuel sprays and combustion is conducted on a light-duty optical engine to investigate the effects of injector aging, with a focus on soot. The spray behaviors of one new and one aged injector are compared using Mie-scattering. In addition to this, the combustion process of a baseline diesel fuel and a blend with TPGME (tripropylene glycol monomethyl ether) are compared using natural luminosity (NL) imaging. TPGME is an oxygenated additive which can be used to reduce soot emissions. X-ray tomography of the two injectors demonstrates that the aging does not lead to significant geometry differences, nor to formation of dense internal nozzle deposits. Both injectors show similar liquid penetration and spreading angle. However, the aged injector shows a prolonged injection and more fuel dribbling after the injection events, leading to a higher injection quantity. The fuel quantity difference shows a larger impact on the NL at low load than the TPGME additive, indicating that the in-cylinder temperature is more important for soot oxidation than oxygen concentration under these conditions. At medium load, the NL is much less sensitive to small temperature variations, while the TPGME is more effective for soot reduction.
Highlights
Modern day diesel injection systems usually consist of a high-pressure fuel pump, and common rail and fast-response diesel injectors
The combustion process of the TPGME soot reducer is investigated against a baseline reference fuel
An X-ray tomography of the injectors eliminates the hypothesis that the aging leads to significant geometric differences in the injector nozzle and needle areas
Summary
Modern day diesel injection systems usually consist of a high-pressure fuel pump, and common rail and fast-response diesel injectors. Faulty or aged injectors can impact the spray patterns and combustion process, leading to reduced efficiency, power loss and high emissions, etc. In addition to the analysis of the various physical influences of aging components, control strategies which focus on identifying and compensating for the aging effects of injectors are studied in several research studies [21,22,23] Such efforts on the research of injector aging all serve the same purpose: ensuring an ideal fuel injection to achieve high efficiency, low emissions and low noise. It was found that the TPGME, as a soot reducer additive, works well, even in an environment with excessive oxygen, but its impact on the combustion process, especially the in-cylinder soot formation and oxidation, remains to be revealed. This work will provide a basis for a combined laser induced incandescence (LII) and laser extinction measurements of in-cylinder soot processes with these injectors and additive in the future
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