Abstract:
Hydrogen is a potential alternative and renewable fuel for homogenous charge compression ignition
(HCCI) engine to achieve higher efficiency and zero emissions of CO, unburned hydrocarbons as well
as other greenhouse gases such as CO2 and CH4. In this study, a detailed hydrogen oxidation mechanism
with NOx was developed by incorporating additional species and NOx reactions to the existing hydrogen
combustion mechanism (10 species and 40 reactions). The detailed hydrogen combustion mechanism
used in this study consists of 39 species and 311 reactions. A reduced mechanism consisting 30 species
and 253 reactions was also developed by using directed relation graph (DRG) method from detailed
mechanism. Developed mechanisms were validated with experimental data by HCCI engine simulation
using stochastic reactor model. Sensitivity analysis was performed to identify the most important reactions in hydrogen combustion and NOx formation in HCCI engine. Pathway analysis was also performed
to analyze the important reaction pathways at different temperatures. Results revealed that H2 + HO2 [=]
H + H2O2 and O2 + NNH [=] N2 + HO2 are the most significant reactions in the hydrogen HCCI combustion and NOx formation respectively. Detailed parametric study of HCCI combustion was conducted using
developed chemical kinetic model. Numerical simulations are performed at different engine operating
condition by varying engine speed (1000–3000 rpm), intake air temperature (380–460 K), and compression ratio (16–18) at different relative air fuel ratios (k). The HCCI operating range was determined for
different compression ratios and results show that operating range expands with increase in compression
ratio. The effect of intake temperature, engine speed and equivalence ratio on cylinder pressure and heat
release rate were investigated. Maximum thermal efficiency of 46% and maximum combustion efficiency
of 98% was observed among all the test conditions. Parametric study of NOx emissions was also conducted and it was found that NOx emissions decrease exponentially from higher to lower engine loads
