Combustion And Emission Formation Mechanisms Of Hydrogen Fueled Internal Combustion Engine Under Diluted Conditions

Hydrogen energy, which is clean, renewable and has multi sources, is regarded as the final energy in the future to deal with energy shortage and the environment pollution problem. Hydrogen fueled internal combustion engine(HICE) is cheap and reliable, so it is the most probably applied method for hydrogen energy used in vehicles. The previous researchers have investigated combustion characteristics of HICEs for a long time. But there are still some questions such as hydrogen-air laminar combustion characteristics under diluted conditions, hydrogen-air chemical reaction mechanism and NOx formation laws have not been explained clearly and reasonable.CO2, which has the large Cp and thermal inertia, is an important component of Exhaust gas of traditional engine. So the EGR gas of traditional engine can dilute fuel-air mixture and decrease the temperature of burned zone in cylinder. But the Exhaust gas of HICE is composed of H2 O and N2. H2 O or N2 has small Cp compared with CO2,. So the EGR of HICE has entirely different mechanisms. This paper investigates the combustion and emission formation mechanisms of HICE under H2 O and N2 diluted conditionsFirstly, laminar combustion characteristics of diluted Hydrogen-Air mixtures are investigated using global shape combustion bomb. The test results show that H2O+N2 and N2 diluted mixture also have much lower laminar combustion speed and temperature in burned zone. Laminar combustion speed and temperature in burned zone are decreased substantially with the diluted rate. Markstein Length is decreased slightly with the diluted rate. It indicates that exhaust gas recycle is a useful method to control NO concentration.Secondly, Hydrogen-air combustion process is investigate using hydrogen-air detailed chemical reaction mechanisms with CHEMKIN software. Then a reduced reaction mechanism with 16 elements and 24 step reactions is got. It is verified that the reduced reaction mechanism can calculate hydrogen-air combustion process accurately with high calculating speed.Then, a three dimension CFD model which involves spray sub model, turbulence sub model, ignition sub model and reduced chemical reaction mechanism combustion sub model is established for simulating of HICE. It is founded that there has a high concentration OH zone in flame. In the first stage of combustion process, high concentration OH zone is spread like a thin wall ellipsoid. Temperature in the flame is always slightly lower than that in burned zone. NO formation is always related closely to temperature of burned zone. Total NO mass in cylinder increasing quickly with flame transmission process. When the combustion is finished, temperature in cylinder decreases slowly, then NO mass in cylinder will decrease with temperature. NO mass will keep steady with temperature when the maximum temperatures lower than 1800 K.It can be found that the maximum average pressure and temperature in cylinder will decrease quickly with the incensement of EGR ratio, and the combustion duration will increase with the incensement of EGR ratio based on three dimension CFD simulations. It in turn reduces NO formation. A four stage continues control strategy with not-high EGR ratio is development for NO concentration control. This control strategy is easy to achieve than the former strategy named“three stage stride across control strategy”...