Experimental Assessment of Ozone Addition Potential in Direct Injection Compression Ignition Engines 2019-24-0118

The potential of ozone addition in compression ignition engines is investigated experimentally in this paper. Experiments were carried out in an optically accessible single cylinder engine equipped with a common rail direct injection system. A commercially available ozone generator (P < 100W) was used to add to the intake flow a controlled amount of ozone.

EU Diesel fuel (cetane number 52) and a Naphtha fuel (cetane number 33) were tested investigating the impact of Ozone in conventional diesel combustion and LTC cases (e.g. high exhaust gas recirculation rate).

Minimal ozone concentration in the intake flow (100 ppm) demonstrated to reduce significantly the ignition delay. However, the impact observed strongly depends on the engine conditions tested and, in general, this effect observed becomes significant in conditions characterized by a long ignition delay: low intake temperature, high dilution, and low cetane number fuel.

Significant practical benefits of ozone addition were found for engine cold-start, where ozone yields a significant reduction in misfire events during the first cycle and a faster stabilization of the combustion phasing and a reduction of the unburned hydrocarbons produced in the warm up phase. Also, a mild increase in the EGR tolerance for low load conditions was achieved (from 2 to5%). Optical diagnostics, such as CH₂O planar laser induced fluorescence and natural chemiluminescence, were applied to understand the physics behind the ozone effects. The results demonstrated that O₃ strongly affects the low temperature combustion phase, causing an earlier development of the chemical reactions. The impact on this phase is eventually reflected in a reduction of the second stage ignition delay, and in a more stable combustion.