Combustion CFD modeling in CNG/H2 fueled IC engines by means of a LFS flame surface-density model

A significant proportion of our daily routine has always been spent traveling from one place to another place. Fossil fuel, particularly petroleum fuel, consumption is steadily rising as a result of population growth which in parallel raises the concerns over the possible environmental issues such as greenhouse gases (GHG) emissions released to the atmosphere that contribute to acid rains and global warming.In order to protect our planet from major environmental challenges that we are likely to face later in this century, some international coordinated efforts have been adopted in order to tackle climate changes. In Paris, on 12 December 2015, 196 Parties to the United Nations Framework Convention on Climate Change (UNFCCC) reached a landmark agreement so-called The Paris Agreement to combat climate change which describes the gravity of this issue. Inevitably the growth of population causes a simultaneous increment in human mobility requirement that leads to the widespread presence of internal combustion (IC) engine which is the power source and mechanical heart sustaining the concept of contemporary mobility.To this issue, automotive sectors made a crucial effort and devoted to a strict de-carbonization process to push the European transport sector to the 2050 target and the use of Low Carbon Alternative Fuels, like Compressed Natural Gas, will play a fundamental role to quicken this process.Natural gas (CNG) is considered as an alternative vehicle fuel because of its economic and environmental advantages which is a clean fuel with CH4 as its major component which produces 20% less CO2 than the other conventional fuel such as gasoline, that is considered to be one of the most favorable fuels for engines. However, due to the slow-burning velocity of CNG and its poor lean-burn capability, the CNG spark-ignition engine still has some disadvantages like low thermal efficiency, large cycle-by-cycle variation, and these decrease engine power output and increase fuel consumption.To improve the lean-burn capability and flame burning velocity of natural gas, one effective method to solve the problem is to blend natural gas with fuel that possesses fast burning velocity engines under lean-burn conditions. Hydrogen is regarded as the best gaseous candidate for natural gas due to its very fast burning velocity and this combination is expected to improve lean-burn characteristics and decrease engine emissions.Alongside the type of fuel which is crucially decisive, there is an effective technique so-called EGR used in IC engines to reduce pollution, specifically to control NOx emissions. However, as the EGR rate at a given engine operating condition rises, the combustion instability increases which produce cyclic variations resulting in the deterioration of engine performance. Therefore, the optimum EGR rate should be carefully determined in order to obtain the better engine performance and emissions.To this aim, the thesis has been conducted to investigate the combustion stability and engine performance for pure CH4 and also CNG blended with different percentages of hydrogen, based on the variation of Indicated Mean Effective Pressure (CoV imep) and MFB50.This work is a consequence of collaboration with engine’s research team at Polytechnic University of Turin composed of master and Ph.D. students, led by professors D. Misul and M. Baratta.