As part of our investigation into biofuels we felt it would be beneficial to perform our own engine testing. Initially our main aim was to try to compare the tailpipe emissions of fossil diesel to that of biodiesel. Unfortunately the gas analysing equipment required was not available to use and so that aim was scrapped. The next aim was to measure the mechanical power available from the engine at a series of set speeds using various blends. Unfortunately the equipment required for this was unavailable. Finally it was decided to run various blends of biodiesel through the engine and attempt to analyse the thermal efficiencies achieved at a set RPM with a set load on the engine. The engine was equipped with a CHP (Combined Heat and Power) rig, which extracts heat from the exhaust gasses.

The engine used was a Lister Petter PJ2W water-cooled, two-cylinder diesel engine. The engine was assembled in such a way as to allow the following measurements to be taken:

Engine Speed
Fuel Flow Rate
Water Jacket Flow Rate
CHP Water Flow Rate
Water Jacket Inlet Temperature
Water Jacket Outlet Temperature
CHP Water Inlet Temperature
CHP Water Outlet Temperature
CHP Exhaust Gas Inlet Temperature
CHP Exhaust Gas Outlet Temperature
Engine Mechanical Power (through the use of a generator driving a two electrical resistance heaters)

From these results it is possible to measure the power lost as heat through the jacket cooling and the CHP rig.

The photo’s below show some of the key components.

The engine itself	The CHP heat exchanger
The fuel tank system	The electrical generator

Actual Testing

During the actual running of the engine only one cylinder was ran as this made it easier to stabilise the engine at a set speed.

The engine was run with biodiesel blends of 0, 10, 20, 40, 60, 80 and 100%.

The procedure for each blend was the same. The engine was adjusted until it was running steadily at 1500rpm long enough to achieve steady state conditions. 15 minutes was given for this. The measurements could then be taken. At least 3 sets of records were taken for each blend and the average of these was then taken.

The results from the testing were disappointing. It was hoped that there would be a clear trends between the 100% fossil diesel and 100% biodiesel. Unfortunately the only reasonably clear trend that developed was the expected rise in fuel consumption.

To maintain a constant engine speed (1500rpm) then it is necessary to input a constant amount of power into the engine in the form of a fuel flow. Since biodiesel has a lower energy content per unit mass than diesel then it is necessary to increase this fuel flow in order to maintain a constant power input. The graphs below shows the power input into the engine over the range of blends.

It can clearly be seen that while the fuel mass flow rate increases with the blend percentage the power input remains fairly constant. It is not unreasonable to suggest that this reflects how a vehicle running biodiesel will have a drop in mileage roughly in line with the drop in energy content.

Regular fossil diesel has an energy content of 45.1 MJ/Kg, compared to 40.8 MJ/Kg for biodiesel. This is a drop of around 10%. The increase in fuel flow rate is also 10% backing up the suggestion that any drop in mileage will be in proportion to the drop in fuel energy content.

The graphs below show the change in power recovery from the jacket cooling and the CHP rig.

From these graphs it is hard to see any trend forming.

The probable reason for the poor results is due to the use of equipment simply not accurate or sensitive enough to measure the relatively small differences between the fuels.

The engine testing itself was overall not very successfull, providing only limited results.

One of the most difficult aspects of the testing was simply getting the engine to run at 1500rpm. The servo which controlled the throttle was jittery and the engine response was very slow. Also, the engine speed was measured with a hand held mechanical tachometer, meaning speed measurments were a little inaccurate.

Although there was equipment to control and measure the engine with a computer, through a program called LabView this equipment was in use elsewhere and was not set up for use with the engine. The result of this is that all the reading had to be taken by hand.

To improve the results of the testing would require more sensitive equipment and flexible computer control. This would allow not only steady state readings but also analysis of the engine during acceleration and deceleration.

Despite these drawback the testing did confirm the effect of the lower energy content of the biodiesel on the fuel consumption rate.