Effect of Additives on Combustion Characteristics of a Natural Gas Fueled HCCI Engine 2014-01-2662
Homogeneous Charge Compression Ignition (HCCI) is among the new generation of combustion modes which can be applied to internal combustion engines. It is currently the topic of numerous studies in various fields. Due to its operating process, HCCI ensures a good efficiency, similar to that of compression ignition (CI) engines, and low particulate and nitric oxide (NOx) emissions. However, before promoting the use of this kind of engine, several challenges must be addressed, in particular controlling the combustion.
Recent work showed that the combustion phasing can be controlled using low concentrations of ozone, an oxidizing chemical species. As ozone generators become increasingly compact, the integration of this kind of device in passenger cars can be considered.
The present study investigates the effect of ozone on the combustion of different fuel mixtures. The engine was fuelled with various blends: a 95%methane/5%propane mixture and three different methane/hydrogen mixtures. The engine parameters and pollutant emissions were analyzed as a function of ozone seeding in several cases: by degrading the intake pressure, by degrading the intake temperature, and by varying the volume fraction in the blend composition to obtain a fuel that auto-ignites less readily. Overall, experimental results showed that ozone improves and advances the combustion of all the fuels considered.
Lastly, computations were conducted using a simple constant volume model to study fuel oxidation in the presence of ozone. Results showed that ozone quickly oxidizes the fuel and is therefore a good combustion promoter.