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GT-Power, an engine modeling software, is used to study the combustion characteristics of cottonseed, linseed and peanut oils in a heavy-duty direct-injection diesel engine. The fuel properties library in GT-Power is expanded to include cottonseed oil, linseed oil and peanut oil, using either theoretical methods or experimental measurements. The numerical model is calibrated with experimental data and good agreement is observed. The simulation results show that combustion characteristics and engine performances differ when vegetable oil is used instead of no. 2 diesel fuel. Raising the injection pressure significantly alters the combustion characteristics without improving the brake performances. However, higher injection pressure does reduce both NOx emission and combustion noise.

A modified KIVA code is used to simulate the operation of a small bore HSDI engine with biodiesel from various sources. Genetic modified soybean biodiesel has very similarly combustion characteristics with soybean biodiesel, albeit less NOx. Yellow grease biodiesel burns in a similar manner as regular diesel with less NOx. All types of biodiesel show longer ignition delay but faster combustion, except after TDC injection, where biodiesel exhibits some diffusion combustion. Delaying injection is an effective way to reduce NOx emission. Over 90% of reduction in NOx is observed when fuel injection is delayed from 335° to 363°.