Usame Demir

An Experimental and Modeling Study to Investigate Effects of Two-Stage Direct Injection Variations on HCCI Combustion

In this study, homogenous charge compression ignition (HCCI) combustion with two-stage direct injection (TSDI) strategies was modeled with stochastic reactor model (SRM) and validated by using the experimental results of the TSDI gasoline HCCI engine. For the experimental study, a diesel engine was converted to an electronically controlled HCCI gasoline engine. The effects of injection timings and injection ratios on the HCCI combustion characteristics were studied at high equivalence ratio and constant engine speed. The injection timings (first and second) and fuel quantity for each injection were adjusted to get desired mixture formation in the cylinder. During the experiments, the maximum cylinder gas pressure, pressure rise rate and start of combustion were directly controlled by using the second fuel injection timing and injection ratio. Using optimal second fuel injection timing and injection ratio caused a reduction on NOx and HC emissions. The model results of the HCCI combustion were in good agreement with the experimental results. Both of the experimental and modeling results showed that the second fuel injection timing had a strong effect on the HCCI combustion when compared to the first injection timing.

Investigation of performance of 0-D internal combustion engine simulation codes based on detailed and reduced chemical kinetic mechanisms

In this study, combustion performance of two 0-D engine simulation codes, Chemkin-Pro and SRM Suite, was examined in a homogenous charged compression ignition (HCCI) engine and comparisons were made against the experimental data, which was based on combustion of TRF-70 (70% toluene and 30% n-heptane in vol. basis). Reduced and semi-detailed chemical kinetic mechanisms of TRF-70 were used in both codes for performance evaluations in terms of pressure, heat release rate and exhaust gas emissions (CO, CO2 and O2). OH and H2O2 emissions, which were difficult to obtain experimentally, were compared computationally among codes using both semi-detailed and reduced mechanisms. Both codes had advantages over the other; stochastic reactor model (SRM) resulted in better results than Chemkin-Pro in terms of pressure and heat release rate when compared to experimental data, while Chemkin-Pro was advantageous owing to its shorter CPU time with acceptable proximity to experimental data.