Dr. Jerald Caton and PhD candidate Junnian Zheng of Texas A&M University report on their use of an engine cycle simulation to evaluate the energy and exergy distribution of various processes in a low temperature combustion (LTC) diesel engine in a paper published in the journal Energy.
Low temperature combustion regimes with high levels of EGR and late injection are of interest because of the potential reduction of both NOx and PM emissions. However, they note, there are few detailed thermodynamic evaluations including second law analysis of the LTC engine.
They first validated their model with experimental data at eight operating conditions including four different EGR levels and two different injection timings. They then used the model to evaluate the effect of EGR level and injection timing on the first and second law parameters.
As EGR was increased, intake temperature and equivalence ratio increased. Results showed that for the case at 0% EGR level with conventional injection timing, about 30% of the fuel exergy was destructed during combustion processes, and as EGR level increased to 45% (intake temperature and equivalence ratio also increased), the combustion destructed exergy decreased to 20% of the fuel exergy. This was largely due to the related combustion temperature increase.
For both conventional (−6.5° aTDC) and late (1.5° aTDC) injection timings, the percentage of exergy transfer through flows increases as EGR increases, which is attributed to the retarded ignition by increasing EGR. Other parameters such as energy and exergy transfer due to heat transfer, blow-by, and unburned fuel also were determined as a function of EGR level and injection timing.
Junnian Zheng, Jerald A. Caton (2012) Second law analysis of a low temperature combustion diesel engine: Effect of injection timing and exhaust gas recirculation, Energy, Volume 38, Issue 1, Pages 78-84 doi: 10.1016/j.energy.2011.12.034