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

In this work, an ozone/air/gasoline mixture has been usedas an alternative strategy to achieve a stable combustion ina spark ignition (SI) single cylinder PFI research engine. Theair intake manifold has been modified to include four cells toproduce ozone with different concentrations. In the researchengine, various operating parameters have been monitoredsuch as the in-cylinder pressure, temperature and compositionof the exhaust gases, pressure and temperature of the mixturein the intake manifold, engine power and torque and specificfuel consumption. Experimental tests have been carried outunder stoichiometric mixture conditions to observe the influenceof ozone addition on the combustion process. The resultsshow an advance and an increase of the in-cylinder pressurecompared to the reference test-case, where a gasoline/airmixture is used. It is worth noting that, especially under stoichiometriccondition, ozone concentration induces auto-ignitionand knock. Thus, the influence of ozone on lean combustionhas been investigated. In particular, the combustionprocess at 1400 rpm under lean conditions, with an air-fuelequivalence ratio around 2, has been tested with varying ozoneconcentrations. The results show a sensible reduction of misfiretogether with a higher laminar flame speed and improved flamestability. Indeed, the ozone addition on air/gasoline mixturereduces the CCV from 5% to 1.75% and an increase of fuelconversion efficiency. Furthermore, pollutant emissions havealso been analyzed. The results show that NOx slightly increaseswhile unburned HCs decrease with ozone concentration.