Part B : Energy Balance on an Engine
and
Engine Performance Mapping
1. Objective
Engines consume fuel and provide power from their output shafts. A portion of the fuel’s
energy is transferred to the engine as heat and must be removed by the coolant. Since the engine
exhaust gases are hot when they leave the engine, some of the fuel energy must be present there
also.
The objective of this experiment is to determine
a) The way in which the fuel energy is distributed after it is burned in the engine.
b) The effect of the fuel/air ratio on this energy distribution.
c) The engine performance characteristics map.
2. Concepts Required
a. Energy and mass balances for combustion applications
b. Properties of ideal gas mixtures
c. Measurement techniques for speed, torque, temperature, pressure and liquid and gas flow
rates.
d. Method for engine performance mapping.
3. Experimental Apparatus
The engine for this experiment is a Kubota R120 diesel engine. This engine is a single
cylinder, four stroke engine with a bore of ______________ and a stroke of ____________. Its
rated power is about 12 hp. The engine is instrumented to allow complete determination of the
energy and mass flows into and out of the engine. The instrumentation will be discussed in detail
during the laboratory period. Special attention should be given to the following:

Torque - The engine torque will be measured with a dynamometer. A dynamometer is a
device for loading the engine to simulate its operation in a vehicle. Our dynamometer can
control the speed of the engine. The dynamometer looks like a large drum. The entire
housing of the dynamometer is mounted in bearings that would allow it to rotate if it was not




held in position by a weight scale. The weight scale measures the force required to restrain
the dynamometer and since we know the distance from the shaft axis to where the force is
applied, the torque can be calculated.
Fuel flow rate - We will be measuring the fuel flow rate using a scale and a stopwatch to get
the average flow rate.
Exhaust temperature - Several measurements of the exhaust gas temperature are available.
We have thermocouples that measure the exhaust gas temperature for your energy balance
calculations.
Cooling mediums temperature - Several measurements of the cooling mediums temperature
are available. We have thermocouples that measure the cooling water and lube oil
temperature for your energy balance calculations.
Air flow rate - The air flow rate is measured with an orifice flow element. This device relies
on the fact that the volume flow rate is linearly proportional to the pressure drop. The
pressure drop is measured and can be converted to a volume flow rate. The volume flow rate
must be multiplied by the density of the air entering the air-box to get the mass flow rate.
4. Experimental Procedure
a. The teaching assistant for your section will start the dynamometer and engine. He will show
you how to set the engine speed on the dynamometer and how to change the engine load.
b. You should run the engine at a moderate power level until the coolant and oil temperatures
stabilize. This typically requires 15-30 minutes. During this period you can familiarize
yourself with the instruments and make some sample measurements. You should make
several practice runs of the fuel flow and coolant flow measurements.
c. You will be running a variable load test. This involves running the engine at a set of fixed
speed at 1200, 1800, and 2400 rev/min, while varying the engine’s output torque. You will
measure the engine’s performance at 100%, 60%, and 20% of full load. Run for at least 10
minutes at each condition before taking any data to be sure that the engine has reached steady
state.
5. Calculations
Use the experimental data collected during this lab period to compute the fraction of the
fuel’s energy that goes to brake work, coolant, and exhaust, and how much cannot be accounted
for. Assume the fuel can be represented by C14.4H24.9 and has a lower heating value of 42,500
kJ/kg.
6. Write-up (Must be typed—sample calculation may be hand written
with units)
Your write-up should include the following items:
a. A table showing the raw data collected in the lab.
b. A table showing the percentage of the fuel’s energy going to work, coolant and exhaust for
each engine operating condition. You should also include a column for the fraction of the
fuel’s energy that is not accounted for.
c. A complete set of sample calculations for one load condition.
d. Plot of the fraction of the fuel’s energy going to work, coolant and exhaust vs. percent of full
load torque.
e. Plot engine performance map.
f. A short discussion (1 page) of the trends observed on the plot. Specifically address the role
that engine friction may play in determining the trends observed.
This discussion should include a statement of any trends that you notice in the data. For example:
Parameter A increased by 12.5% as the speed was increased from 600 to 1200 rpm.
The discussion should note any deviations from the trends or abnormalities that occurred during
the test. For example:
Parameter B stayed constant for the 15 minute duration of the test, except for a 2% drop during
the last 2 minutes.
The discussion should explain the trends when possible. These explanations may include
speculation if it is clearly identified as such. For example:
The 8% rise in oxides of nitrogen emission may have been caused by the 10C rise in engine
intake air temperature.
Finally, provide recommendations for improvements that could be made in the experiment that
would provide more accurate or useful information.
Your lab write-up should always include the day and time your lab meets. All material submitted
as part of the lab write-up should be professional in quality. All figures and tables should be
numbered and have titles. Refer to the figure and table numbers during your written discussion.