An Experimental Characterization of Gasoline/Ozone/Air Mixtures in Spark Ignition Engines

In this work, an ozone/air/gasoline mixture has been used as an alternative strategy to achieve a stable combustion in a spark ignition (SI) single cylinder PFI research engine. The air intake manifold has been modified to include four cells to produce ozone with different concentrations. In the research engine, various operating parameters have been monitored such as the in-cylinder pressure, temperature and composition of the exhaust gases, pressure and temperature of the mixture in the intake manifold, engine power and torque and specific fuel consumption. Experimental tests have been carried out under stoichiometric mixture conditions to observe the influence of ozone addition on the combustion process. The results show an advance and an increase of the in-cylinder pressure compared to the reference test-case, where a gasoline/air mixture is used. It is worth noting that, especially under stoichiometric condition, ozone concentration induces auto-ignition and knock. Thus, the influence of ozone on lean combustion has been investigated. In particular, the combustion process at 1400 rpm under lean conditions, with an air-fuel equivalence ratio around 2, has been tested with varying ozone concentrations. The results show a sensible reduction of misfire together with a higher laminar flame speed and improved flame stability. Indeed, the ozone addition on air/gasoline mixture reduces the CCV from 5% to 1.75% and an increase of fuel conversion efficiency. Furthermore, pollutant emissions have also been analyzed. The results show that NOx slightly increases while unburned HCs decrease with ozone concentration.