Abstract: Based on the third edition of Lawrence Livermore National Laboratory (LLNL) n-heptane oxidation detail model, the chemical kinetics simulation was conducted using the parameters of a 4100QBZL-2 DI engine. The ignition delay time was investigated and simulated, with the engine fueled with 0%(pure diesel), 10%, 20% and 30%(by volume fraction) water-diesel emulsion. The chemical kinetics calculation results were compared with the experimental results and the computational fluid dynamics coupled with n-heptane reduced model (CFD-SKLE) calculation results. The results indicated that, the ignition time was delayed due to the physical phenomena of water in emulsified fuel. From a chemical view, the water in emulsion fuel can promote the formation of free radicals H, O, OH, HO2 in n-heptane's low temperature reaction regime (cool flame). Those free radicals can create advantageous conditions for n-heptane high temperature reaction (hot flame) and advance the ignition timing. The sensitivity analysis results of n-heptane oxidation with water showed, the water will promote isomerization of alkyl peroxide and decomposition of hydrogen peroxide ketones in n-heptane low temperature reaction regime and consequently accelerate the n-heptane oxidation chain reactions.