Experimental Study of Using EGR to Raise the Thermal Ratio of Methanol to Diesel Fuel in Diesel Engine 931950

Using methanol to replace the diesel fuel in diesel engine is a simple way in using of alternative fuel. But the main problems are that the max. cylinder pressure and the cylinder pressure rising will be increased. This increases the mechanical load engine noise and affects the engine reliability. Also limits increasing the ratio of methanol to diesel fuel. This paper presents an new way of using EGR to control the cylinder pressure and to raise the ratio of methanol to diesel fuel.

There are many ways to burn methanol in diesel engines. Generally, the liquid methanol is vaporized by heating of exhaust pipe or and cooling water, then it mixes with air through intake pipe, finally, burns in the cylinder. The advantages of this method are that the structure of diesel engine needs no change. By using the exhaust heat to vaporize the liquid methanol, the wasted heat can be utilized again. So it is helpful to improve the thermal efficiency. However, there are some shortages. If the ratio of methanol to diesel fuel increases, the engine economy may become bad at low load and the knock may occur at high load. Furthermore, the rapid cylinder pressure rising and the excessive maximum pressure will increase the mechanical load. In some worse case, it will even damage the cylinder wall. Thus the working life and reliability of the engine will be reduced. Those disadvantages limits the increasing of methanol to diesel fuel ratio.

The authors successfully use the EGR to control the maximum cylinder pressure and the pressure rising rate for increasing the ratio of methanol to diesel fuel. Some evaulating methods and indexes about the ratio of methanol to diesel fuel and EGR are also presented.