Mechanical Engineering Principles (ENG414) Efficiency of a Simple Internal Combustion Engine Lab Report
Gabriel Zani
Date Experiment Performed: 17/10/2013 Date Report Submitted: 05/11/2013
Introduction This laboratory experiment is being conducted to study the behaviour of an internal combustion engine under different operational conditions. An internal combustion engine is a mechanical device uses chemical energy stored in a fuel (liquid or gas) as a source to convert into mechanical energy. Expansion of high pressure and high temperature gasses produced by combustion of fuel inside the internal combustion engine cylinder convert some energy into work by moving the engine piston; hence, this force of moving the engine piston over a distance result in converting chemical energy into useful mechanical energy (Salazar, 1998). There are four repeating steps for this process to be achieved, namely: air and fuel intake, compression of air and fuel mixture, combustion and exhaust gases (NSW Derpartment of Education and Trainning , 2008). Internal combustion engines are usually used in mobile applications such as aircrafts, boats and cars.
Aim The aim of this experiment is to understand and familiarize the principal features of a simple internal combustion engine. Power and efficiency of the internal combustion engine under a range of masses are being observed, studied and compared.
Background and Analysis The internal combustion engine used in this experiment is a Ruston & Hornsby single cylinder, horizontal engine that operates on a four stroke compression ignition cycle. Reciprocating motion of the piston is converted to rotary motion by the crankshaft and connecting rod. A band is being placed on the brake drum, with weights hanging at each end of the band in balance. The friction caused between the band and the rim of the drum absorbed the engine power and which, is being measured by using a spring balance. Vibrations caused by cyclic variations in the engine speed are being supressed by a hydraulic damper which attached to one
end of the band. The temperature of the rim is controlled and kept steady by filling the groove inside the rim with water. The water helps to absorb and dissipate the heat that is generated by evaporation. Fuel is placed into a transparent cylinder with a measurement of 50ml increment. Therefore, consumption of a specific amount of fuel flow rate can be timed by using a stopwatch, in this case, 50ml. The flow from the main fuel tank is being shut off during the measurement. It is essential to turn on the flow at the end of the measurement to avoid the fuel line fill with air. Fuel line fill with air will result in engine shut down, causes it to become a necessity to bleed the fuel system before the engine can be restarted.
Methods 1. The Ruston & Hornsby engine is started and operated by a member of staff by using a burning source to ignite the fuel and manually rotating the lever to automate the cyclical combustion engine process. 2. A heavy load is applied to the engine to hasten warm-up. 3. The engine is adjusted by a speeder spring to keep a constant speed of 450 rev/min, so that each masses variable will have an equivalent speed of the engine. 4. The groove inside the rim is being filled with water to provide a constant temperature thought out the experiment. 5. Mass load m1 will be equal to mass load m2 for easy calculation. Mass loads m1 = m2 are started with 60 lbs. 6. The reading of spring balance and the time taken to consume 50ml of fuel for the mass load m1 = m2 are obtained. 7. Repeat step 5 and 6 by using mass load m1 = m2 with 40, 20 and 10 lbs. 8. Calculate the torque, power, energy input rate and efficiency by using the constant provided (brake drum radius, fuel density, etc.) and the result obtained from the experiment.
Mass load, m1=m2 (kg)
Brake Torque, T= Sr (Nm)
89.19 59.46 29.73 17.34
Time to Consume 50 ml Spring Balance, S Fuel, t (s) (N) ± 2s % Error ± 1N % Error 27.22 125 1.6 180 0.56 18.14 157 1.27 120 0.83 9.07 217 0.92 60 1.67 Brake Thermal 4.54 Power, Fuel 256Energy Input 0.78 Rate, Brake 35 2.86 Efficiency, ´ W ´ b = 2 πNT ηtb = b × 100 (%) ´ f = ρf V f C f W Q ´f (W) 60 Q t (W) 4202.98 2801.99 1400.99 817.25
14226.24 11326.62 8194.84 6946.41
29.54 24.74 17.10 11.77
Results
.
Table 1: Raw Data with Estimated Uncertainties .
.
Table 2: Derived Data Results Time taken errors are estimated at ±2s while spring balance errors are estimated at ±1N. Since theoretical value cannot be calculated for this experiment, the percentage of error is calculated by Estimated Error × 100 using Experimental Value .
lbs are being converted to kg by using
lbs 2.204622476
.
T= Sr, where r is the brake drum radius, 0.4955m. ´ b = 2 πNT W , where N is the desired engine speed, which is 450 rev/min. 60 ´ f = ρf V f C f Q , where t and
Cf
ρf
is the fuel density, 840 kg/m3,
is the fuel calorific value, 42.34 MJ/kg.
Vf
is the volume of fuel, 50ml
Data Plotting Brake Power (Ẇb) against Brake Torque (T) 4500 4000
f(x) = 47.12x + 0.09 R² = 1
3500 3000 2500
Ẇb (W) 2000 1500 1000 500 0 10
20
30
40
50
60
70
80
90
100
T (Nm)
´ Graph 1: Brake Power ( W b ) against Brake Torque (T)
Brake Thermal Efficiency (ƞtb) against Brake Torque (T) 35 30
f(x) = 0.24x + 8.94 R² = 0.97
25 20
ƞtb (%) 15 10 5 0 10
20
30
40
50
T (Nm)
60
70
80
90
100
Graph 2: Brake Thermal Efficiency (ƞtb) against Brake Torque (T)
Discussion Based on graph 1, brake power is directly proportional to the brake torque. This linear 60 ¿ relationship can be observed from the equation T = ( 2 πN Ẇb. Graph 1 is a straight line with a gradient of 15π (47.12). The brakes torque increased, the brake power increased. Based on graph 2, when the brake torque increased, the brake thermal efficiency also increased. This is due to when brake torque increased, brake power will be increased (proven by graph 1), and henceforth, when less energy is lost to the surrounding, the efficiency increased. The graph is an exponential graph due to the limitation of internal combustion engine. For a stock engine, only 20% of the power in fuel combustion is effective (Newman, 2002). Inaccurate results were deemed to be the result of experimental errors. One of the errors in this experiment was human error. The time taken for each 50ml fuel of fuel consumption was based on the student’s justification of the reading on the fuel tank and his/her reaction on the stopwatch. Hence, two flaws were being introduced into the system. Human errors such as parallax errors occurred during rod reading. The eyes position are not perpendicular to the reading of the instrument can lead to inaccurate data recorded due to the expected discharge 50ml of fuel did not achieve. Moreover, without precise mechanical measurement tool or proper scaling on the fuel tank, measuring based on the gap within the fuel tank will result in an approximation of 50ml of fuel. Time taken was exclusively base on the reaction of the student, thus, introduced an error of time taken which were being delayed or advanced. To obtain an exact of 50ml fuel consumption and time taken for it, fuel management systems or digital sensors with real time monitoring software could be installed to provide a more accurate data. Instrumental error can be occurred during the experiment. When taking the spring balance readings, the analogue display values were fluctuating, unstable and keep on changing. In order to minimise this error, reading should be taken after the reading is stable. The experimental data may also have been influenced by the oil, as in the oil might contain impurities which will affect the combustion of the engine; if necessary, an overhaul should be performed. A suggested
improvement is to repeat the experiment with improve and enhance equipment so as to have more readings in the same set and therefore, calculate the mean of the readings. Spring balance readings errors are estimated to be ± 1N. Due to the spring balance data are being carried forward for the calculation of brake torque and brake power, both of them shared the same percentage of errors of the same mass load with the spring balance. Since the highest percentage of error for the spring balance is 2.86%, the maximum error in the graph 1 will be 2.86%. Time taken errors for 50ml of fuel to be consumed are estimated at ± 2s. Due to the time taken data are being carried forward for the calculation of fuel energy input rate and brake thermal efficiency, both of them shared the same percentage of errors of same mass load with the time taken for 50ml of fuel to be consumed. Since the highest percentage of error for the time taken is 1.6%, the maximum error in graph 2 will be 1.6%.
Conclusion In conclusion, this experiment was a success as the aim is being achieved; principal features of a simple internal combustion engine are being understood and the brake power and brake thermal efficiency of the engine are being obtained. Brake thermal efficiency obtained was 29.54%. It indicated that only 29.54% energy produced by the engine was converted into mechanical energy while the rest were being dissipated as heat energy into the surrounding air or to operate other valves and parts of the engine. An internal combustion engine will not produce 100% of efficiency; it needs to overcome engine friction and pumping the air and fuel (University of Washington, 2013). The results obtained are accepted. Suggestions are made to improve the experiments.
Bibliography Newman, D. (2002). The Efficiency of the Internal Combustion Engine. Retrieved from http://ffden2.phys.uaf.edu/102spring2002_Web_projects/Z.Yates/Zach%27s%20Web%20Project %20Folder/EICE%20-%20Main.htm NSW Derpartment of Education and Trainning . (2008). Inspect and Service Engines. Retrieved from Automotive Trainning Board : http://www.atbnsw.com.au/files/09/Inspect%20and%20Service %20Engines.pdf Salazar, F. (1998). Internal Combustion Engines. Retrieved from University of Notre Dame: http://www3.nd.edu/~msen/Teaching/DirStudies/Engines.pdf University of Washington. (2013). University of Washington . Retrieved from UW Courses Web Server: http://courses.washington.edu/me341/oct22v2.htm
