The Effect of Increased Fuel Intake Temperature on the Performance of Internal Combustion Engines

The objective of this research is to study how the increase in intake fuel temperature
affects the performance of internal combustion engines. The heat source to input the
heat to the fuel intake comes from unwanted heat source such as exhaust gas or the
radiator coolant for which a prototype heat exchanger was designed and built. Increased
fuel intake temperatures for internal combustion engine are expected to produce more
power and improve on fuel economy. The study of this research is limited to only two
types of engines; a 1800cc 4-cylinder, 4-stroke, fuel injection gasoline engine and a
1800cc 4-cylinder, 4-stroke diesel engine. Both engines are used for analytical
calculations. Due to unavailability of the gasoline engine, only the diesel engine is used
for experimental runs. Fuel intake for each engine is preheated before entering the
cylinder. This is done by directing the fuel to a heat exchanger, which its temperature is
able to be controlled, and heat the fuel up to about 70 degrees Celsius. A heating coil
substitutes the role of unwanted heat source in the engine bay as this simulates the actual
condition in the engine bay and it is simpler to manipulate for experimental purposes.
Theoretically, net work output will be increased as the heat input in the combustion
cycle is increased with the increase temperature and energy in the fuel. Analytical
results have shown that with certain assumptions, net work output has been increased
slightly due to the increase in temperature of fuel intake. 0.97% increment is calculated
for gasoline engine and 0.85% increment is calculated for diesel engine. However,
experimental runs on increased fuel intake temperature have shown adverse effects on
the torque and power output for the diesel engine. A significant drop of torque output up
to 50% and a drop of BHP up to 65% are observed for 50% throttle position while a
drop of torque and BHP up to 20% is observed for 100% throttle position. A few
possible reasons are identified but the true reason behind it requires further research in
the future and is out of the scope of this study. The experimental heat transfer rate of this
heat exchanger ranges from 0.3kW to 1.1kW, depending on the flow rate. Higher flow
rate provide more heat transfer rate as there is less heat loss during transmission while
low flow rate provides less heat transfer rate.