Performance test of compression ignition engine...
Performance Test of Compression Ignition Engine Michael Adrian Vallecera Ygnacio1
Abstract: Internal Combustion (IC) engines are widely used in the automobile industry and ever since its creation, the demand these engines are growing each year. However IC engines are known to be pollutants and one of the major culprits to climate change due to the harmful exhaust gases these engines emits. Thus the need to produce efficient and economical engines arise. It is known that engines that are efficient and working at high performance shows lesser emissions. This study investigates the CI engine’s operation performance. In this study, the effects of varying the load and throttle positions under load and without load was also determined. The torque produced by the engine, specific fuel consumption, engine speed and temperatures were gathered. These parameters are needed in order to determine the efficiency of the Diesel Engine. Author keywords: Diesel engine; Engine performance: Combustion; Engine operation
Introduction The growing concern on environmental pollution caused by the extensive use of conventional fossil fuels has led to search for more environment friendly and renewable fuels. Among various options investigated for diesel fuel, biodiesel has been reported to be one of the strong contenders for reductions in exhaust emissions. (Raheman, 2008) Diesel engines are widely used in a variety of vehicles due to their high fuel efficiency and low cost compared to other fuel engines. The Diesel engine is also known as a compression-ignition or CI engine. Compression ignition (CI) engine often called diesel engine plays an important role in transportation and power generation because of their high efficiency, affordability, and reliability (Iorio et al. 2016). The diesel engine is an internal combustion engine in which ignition of the fuel that has been injected into the combustion chamber is caused by the high temperature which a gas achieves when greatly compressed (adiabatic compression). This contrasts with spark-ignition engines such as a petrol engine or the gasoline engine, which use a spark plug to ignite an air-fuel mixture. In diesel engines, glow plugs may be used to aid starting in cold weather, or when the engine uses a lower compression-ratio, or both because it serves as a pre-warmer to the combustion chamber.
Student, Dept. Mechanical Engineering, Univ. of San Carlos, Cebu City 6000, Philippines, E-mail:
[email protected] The diesel engine has the highest thermal efficiency or the engine efficiency of any practical internal combustion engine due to its very high expansion ratio and inherent lean burn which enables heat dissipation by the excess air. A small efficiency loss is also avoided compared to two-stroke non-directinjection gasoline engines since unburnt fuel is not present at valve overlap and therefore no fuel goes directly from the intake/injection to the exhaust. Low-speed diesel engines, as used in ships and other applications where overall engine weight is relatively unimportant, can have a thermal efficiency that exceeds 50% The performance of any internal-combustion engine, irrespective of its operating cycle, is primarily a function of the thermal energy liberated per cycle, the part of the cycle in which it is liberated, the compression ratio, and the mechanical limitations imposed by the engine structure. (Rothrock) For a given compression ratio the thermal efficiency of the Otto cycle would be greater than the thermal efficiency of the Diesel cycle. However it must be remembered that the Diesel cycle operates on a much higher compression ratios than SI engines (12 to 24 versus 8 to 11) and thus have higher thermal efficiencies. (Pulkrabek) Engine performance is an indication of the degree of success of the engine performs its assigned task, i.e.
the conversion of the chemical energy contained in the fuel into the useful mechanical work. The performance of an engine is evaluated on the variables like indicated power, brake power, brake specific fuel consumption, exhaust emissions, cooling of engine, maintenance. (Arante, 2014)
maximum capacity. The fuel filter was checked and ensured to be clean. The fuel tank was refilled with the diesel fuel.
Experimental Methods Apparatus
Engine Start Up
Fig. 1 shows the test set-up available in the USC-TC ME laboratory. The engine and other equipment are already fixed and properly set up in the lab for the purpose of determining the necessary parameters in obtaining the performance of the compressionignition engine (CI engine). The compressionignition engine was coupled with a dynamometer wherein it can measure the torque of the CI engine. An elevated water tank placed near the set-up supplies the water to the dynamometer. That water from the water tank flows to the water absorber and exits through a hose and into the drain. The control panel displays the torque, engine speed, exhaust temperature and inlet temperature of the air.
The battery was connected to the starter of the CI engine. A wrench was used to secure the wires to the battery. The wires were connecter to the correct polarity of the battery. Fuel was supplied to the engine by opening the valve. The recoil rope was pulled several times while pressing down the choke to relieve friction between the mechanical parts of the engine. The throttle was set to the desired position. The choke was set downwards before starting the engine. An extension wire was needed to supply electricity to the control panel. It was then turned on and the reset button was pressed in order to reset the data. The key was inserted and the engine is turned on.
Data Gathering
Fig. 1. Compression-Ignition Engine Setup Schematic Diagram (Source: Arante, Laurente, Villamor, 2014)
Preparation before the Experiment Before the engine or the experiment itself starts, the laboratory windows were opened. An electric fan was also placed near the exhaust of the engine to direct the exhaust gases of the engine out of the room since these gases contain harmful elements that could affect the health of the students. The water tank was filled with water up to the mark that shows half of its
Initially, no load was applied by tightly closing the water inlet valve in the dynamometer coming from the water supply tank. At 25% throttle, we started at 1400rpm and gathered the data available in the control panel. The torque values were varying up and down so much. The fuel consumption was attained based on the amount of time (in seconds) the certain amount of fuel is consumed by the engine. In this experiment we timed as to how many seconds the engine can consume 10mL of fuel. Ambient temperature and the exhaust temperature can be gathered directly in the control panel in the CI engine setup. These are labelled T1 and T2 respectively. Load was slowly applied to the engine by opening the water inlet valve until we reach the designated speed of the engine. The throttle was adjusted to three different throttle positions (25%, 50% and 75%) and 4 engine speeds each throttle position. A difficulty was encountered in attaining the required speed as there is a lag in the engine response when the load is applied. After the data were gathered, the efficiency was computed
Results and Discussion
Brake Power An IC engine is used to produce mechanical power by combustion of fuel. Power is referred to as the rate at which work is done. Power is expressed as the product of force and linear velocity or product of torque and angular velocity. In order to measure power one needs to measure torque or force and speed. The force or torque is measured by Dynamometer and speed by Tachometer. The power developed by an engine and measured at the output shaft is called the brake power (bp) and is given by:
P=2 πTN (1) where: P = Brake power
N = Engine speed
T = Torque produced by the engine.
Fig. 2. Typical Power & Torque vs engine RPM curve of a typical automobile engine. (Retrieved from: https://www.quora.com/Why-is-it-that-the-output-torqueof-an-engine-starts-reducing-after-reaching-a-peak-eventhough-the-RPM-is-increasing)
The result that we obtained in this experiment is shown in Fig. 3. The graph shows the power at the three different throttle position versus the corresponding engine speeds. Apparently, the graph that we obtained based on the data we gathered just shows the part of the graph where the power begins to fall or decrease again as seen in Fig.1.
Fig. 2 shows the typical power and torque vs. engine speed curve. As seen on the graph, the power of the engine slightly increases as the engine speed increases. This is because if the throttle setting is higher, its means that the engine speed is also higher. Based on equation 1, the brake power of an engine is proportional to the increase of the speed. However the graph also shows that the maximum power and torque that the engine yields is located at a certain point and then drops back down as the speed increases further.
Power (kW)
POWER VS. SPEED 5 4 3 2 1 0 00 00 00 00 00 00 00 00 00 00 00 1 1 12 13 14 24 26 28 30 32 34 36
Speed 25%
50%
75%
Figure 3 POWER VS SPEED
Heating Value of Fuel Energy input to the system is the chemical energy of fuel, which is calculated as the following (Kopac and Kokturk, 2005; Caliskan et al., 2010)
Qf =Qmf LHV (2) where: Qf= combustion heat from fuel (kW) Qmf= fuel consumption (kg/sec)
LHV = lower heating value of fuel (kJ/kg) = 43400kJ/kg
Brake Power VS. Thermal Efficiency 25
Thermal Efficiency
The heating value of a fuel is determined by the amount of fuel and the lower heating value of fuel. The heating value of fuel also determines the amount of chemical energy that the fuel can transmit and convert into mechanical power. If more fuel is fed to the engine, more power is attained by the engine because the greater the heating value, the greater the power it yields. Fig. 4 shows the graph between Power and the heating value of the diesel fuel used in the duration of the experiment.
20 15 10 5 0 12 17 .3 36 06 08 03 .6 15 44 25 09 0. 0. 0 0. 0. 0. 1. 1 0. 3. 4. 4.
Brake Power (kW)
Power (kW)
POWER VS. HEATING VALUE OF FUEL 6 4 2 0
25%
50%
75%
Fig. 5 Brake Power VS. Thermal Efficiency
QF (kW) 25%
50%
Figure 5 shows the graph between Brake power and the thermal efficiency of the CI engine based on the data we gathered during the experiment. It can be observed that as the brake power increases, the thermal efficiency also increases.
100&
Fig. 4 Brake Power VS Heating Value of Fuel
Brake Thermal Efficiency Conclusions Thermal efficiency is the measure of the efficiency and completeness of combustion of the fuel, or, more specifically, the ratio of the out-put or work done by the working substance in the cylinder in a given time to the input or heat energy of the fuel supplied during the same time. The brake thermal efficiency can be determined from:
ηbt = where:
P Qf
(3)
ηbt = brake thermal efficiency P= brake power
Qf = combustion heat of fuel. Engines can have indicated thermal efficiencies in the range of 50% to 60%, with brake thermal efficiency with about 30%. Some large, slow CI engines can have brake thermal efficiencies greater than 50% (Pulkrabek).
At one point closer to the engine’s upper RPM limit, the power peaks and starts to reduce as the rate of fall in torque is greater than the rate of increase in RPM. Varying the engine speed of the CI engine has revealed that in every throttle setting there exist a point where the efficiency of the CI engine will be optimal It is the condition where the CI engine is at its highest and most efficient. The speed and torque is directly proportional to the speed until it reaches the optimum point and then both will drastically fall back one the speed increases further from the optimum point. The highest efficiency the engine reached during the experiment was only 21% when the throttle position was at 75%.
Notations The following symbols are used in this paper:
Bsfc LHV N
Pulkrabek, W. “Engineering Fundamentals of the Internal Combustion Engine”. 2nd Edition, 91-94.
= break specific fuel consumption = lower heating value (kJ/kg)
Sing, H. (2012). “Thermodynamics II- IC Engine Testing”. Govt. Polytechnic College Batala
= engine speed (rpm)
P = engine brake power (kW)
Qf
= heating value of fuel (kW)
Qmf
= fuel consumption (kg/s)
Qvf =¿ T
= torque (Nm)
ρf =¿ y bt
volume of fuel used (m3/s)
diesel fuel density (
0.84
kg L
)
= break thermal efficiency
References Abdulhadi, M. and Hassan, A. “Internal Combustion Engines”. p.5. Arante, M., Laurente, M., Villamor, L. (2014). “Performance Test of CI Engine”. p. 11 Caliskan H., Tat M.E., and Hepbasli A. (2009). Performance assessment of an internal combustion engine at varying dead (reference) state temperatures, Appl Therm Eng, 29, 3431-36. Kopac M., and Kokturk L., (2005). Exergy Determination of optimum speed of an internal combustion engine by exergy analysis, Int. J. Exergy Kachhad M. and Vegad G. (2006). “Study and Testing of CI engine by Rope Brake Dynamometer. pp. 3-5.
APPENDIX
Table 1. Throttle position at 25% SPEED
Heating Value Fuel (Qf) (kW)
TORQUE(N-m)
POWER (kW)
EFFICIENCY
1400
2.2928
0.84
0.1232
5.37
1300
2.352
1.24
0.1688
7.18
1200
3.1428
2.37
0.2978
9.47
1100
3.255
3.1
0.3571
10.97
Table 2. Throttle position at 50% SPEED
Heating Value Fuel (Qf) (kW)
TORQUE(N-m)
POWER (kW)
EFFICIENCY
3000
4.6698
0.19
0.05969
1.2782
2800
4.9936
0.27
0.07917
1.5854
2600
9.5936
3.8
1.0346
10.7842
2400
12.152
6.4
1.60085
13.2365
Table 3. Throttle position at 75% SPEED
Heating Value Fuel (Qf) (kW)
TORQUE(N-m)
POWER (kW)
EFFICIENCY
3600
5.2076
0.4
0.1508
2.8958
3400
15.8505
9.66
3.4394
21.699
3200
28.0429
12.68
4.2491
15.1521
3000
33.142
13.03
4.0935
12.3514
