Purpose of Testing an I.C. Engine:
In general, the purpose or significance of testing an I.C. engine is to determine the following:
(i) To determine rated power output with respect to the fuel consumption in Kg per
Kw-hr of brake power output.
(ii) To determine the mechanical and thermal efficiencies of the engine.
(iii) To see the performance of the engine when loaded at different loads.
(iv) To determine the quantity of lubricating oil required per bp Kw hr.
(v) To determine the quantity of cooling water required per bp Kw hr.
(vi) To determine the overload carrying capacity of the engine.
(vii) To prepare the heat balance sheet of the engine.
In short it is the maximum power available from the expanding gases developed by combustion of fuel within the cylinder; neglecting frictional losses, mechanical losses and loss due to heat and enthalpy.
Which means this is the theoretical maximum and actual power developed within the cylinder that never reach completely to the crankshaft.
Brake Power, bp = (W−S) x 2𝝅( 𝑫+𝒅𝟐 )xN 𝟔𝟎𝒙𝟏𝟎𝟎𝟎 kW
Measurement of friction power by Willan’s line method:
Willan’s line method is also known as the fuel rate extrapolation method. In this method, we draw a graph where we take brake power (B.P)(kW) on X-axis and fuel flow rate (kg/hr) on Y-axis on a condition that the engine is running at a constant speed.
As shown in the figure, the graph is anticipated back to zero fuel flow rate of zero fuel where it cuts at point A on the negative X-axis.
Point A on the negative X-axis shows the friction power at the same speed on the engine. When break power becomes zero, then fuel consumption at the same power represents the fuel consumed to overcome the friction loss of the engine.
As per the graph, variation in the fuel flow rate and brake power is linear. It results in the anticipation of the straight part of the main curve as a negative crossing on the X-axis at zero fuel flow rate will represent the friction power (F.P).
Limitations of Willan’s line method:
Measurement of friction power by Morse test:
I1+I2+I3+I4 = (BP)engine +(F1+F2+F3+F4)
Where I1, I2, I3 and I4 – Indicated power of four cylinders
(BP)engine – Brake power of engine when all cylinders are working
F1, F2, F3, F4 – Frictional power of all four cylinders
Then the first cylinder is cut off by short circuiting spark plug in case S.I. engine (or cutting fuel supply in case C.I. engine). This causes the speed to drop due to non-firing of first cylinder. It should be noted that although first cylinder is not producing power still it is moving up and down so its frictional power must be considered. This speed is once again maintained to its original value by reducing load on the engine
I2+I3+I4 = (BP)2,3,4 +(F1+F2+F3+F4)
Where (BP)2,3,4 – Brake power of 2,3 & 4 cylinders only.
Repeat the above procedure for remaining cylinders and calculate I.P. of the engine.
Cylinder 2 is cut off – I1+I3+I4 = (BP)1,3,4 +(F1+F2+F3+F4)
Cylinder 3 is cut off – I1+I2+I4 = (BP)1,2,4 +(F1+F2+F3+F4)
Cylinder 4 is cut off – I1+I2+I3 = (BP)1,2,3 +(F1+F2+F3+F4)
I.P. of cylinder 1 is calculated as,
I1 = (BP)engine – (BP)2,3,4
Similarly, I2, I3 and I4 is calculated as follows
I2 = (BP)engine – (BP)1,3,4
I3 = (BP)engine – (BP)1,2,4
I4 = (BP)engine – (BP)1,2,3
Total Indicated power of engine = I.P.
IP = I1+I2+I3+I4
Frictional power of engine
FP = IP – (BP)engine.
Mean effective pressure is a quantity relating to the operation of a reciprocating engine and is a valuable measure of an engine's capacity to do work that is independent of engine displacement.
where:
pme – mean effective pressure
W – work performed in a complete engine cycle
Vd – engine (cylinder) displacement
we can write the expression of the engine work as:
There is also a direct relationship between the power of the engine and the work produced:
where:
nr – number of crankshaft rotations for a complete engine cycle (for 4-stroke engine nr = 2)
P – engine power
ne – engine speed
The mean effective pressure function of power and engine speed:
Power is the product between torque and speed:
we get the expression of mean effective pressure function of engine torque:
Brake thermal efficiency is defined as break power of a heat engine as a function of the thermal input from the fuel. It is used to evaluate how well an engine converts the heat from a fuel to mechanical energy
The thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, for example engine, a steam turbine, a steam engine, a boiler, a furnace, etc., Thermal efficiency indicates the extent to which the energy added by work is converted to net heat output.
Mechanical efficiency is the measure of effectiveness of a machine's energy and power that is input into the device into an output that makes force and movement. Mechanical advantage by comparing the input and output force you can find the advantage of a machine
Volumetric efficiency in internal combustion engine engineering is defined as the ratio of the mass density of the air-fuel mixture drawn into the cylinder at atmospheric pressure (during the intake stroke) to the mass density of the same volume of air in the intake manifold.
Thrust specific fuel consumption (TSFC) or sometimes simply specific fuel consumption, SFC, is an engineering term that is used to describe the fuel efficiency of an engine design with respect to thrust output.
mf = mass of fuel supplied in kg/min.
c = calorific value of fuel in kJ/kg
then heat supplied = mf 
c
B. Heat output comprises of heat expenses,
Heat expenses are
brake power of the engine,
B.P. = 
in watts (neglecting diameters of ire rope)
B.P. = 
in watts (considering diameters of ire rope)
b. heat rejected to the cooling water
mw = mass of cooling water supplied (in kg/min)
Cpw = specific heat of water which may be taken as 4.187 (in KJ/kg.k)
Tw1 = Inlet temperature (in 0 C or K)
Tw0 = outlet temperature (in 0 C or K)
mw 
Cpw 
(Tw0 - Tw1) (in KJ/min)
c. Heat carried away by exhaust gases
meg = mass of exhaust gasses in kg/min
Cpeg= specific heat exhaust gases in kj/kg.k
T = Rise in temperature in 0 C or K
Then heat carried away by exhaust gases
= meg Cpeg
T in KJ/min
= meg Cpeg(Teg – Ta)
Where Teg = temperature of exhaust gases
Ta = atmospheric room temperature
d. Unaccounted heat
Heat balance sheet on minute basis is present as below
KJ/min | % | Heat output | KJ/min | % | |
|
| 100% |
|
|
|
|
|
| b. Heat rejected to cooling water |
|
|
|
|
| c. Heat carried away by exhaust gases |
|
|
|
|
| d. Unaccounted heat |
|
|
Necessity of heat balance sheet
due to several reasons and allows to think of the method to reduce the heat energy losses so incurred.
Driving cycles are extremely important in establishing compliance of emission control norms for vehicles. Internationally, it has been observed that there are considerable differences between the driving conditions of type-approval cycles and those of real-world vehicle use. This leads to real-world emissions being higher than expected.
Emission standards:
Emission standards are requirements that set specific limits to the number of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles (motor cars) and other powered vehicles but they can also regulate emissions from industry, power plants, small equipment such as lawn mowers and diesel generators. Vehicle emission performance standard: An emission performance standard is a limit that sets thresholds above which a different type of emission control technology might be needed.
Technology | Emission | Significance |
Fuel injection | Fuel consumption and particulate emissions | The shift from port injection to gasoline direct injection (GDI) was driven by the use of engine downsizing to meet fuel consumption and CO2 requirements. GDI engines have a higher tendency to produce small particle emissions that can be partially offset by refinements in fuel injection system design. |
Intake boosting | Fuel consumption | Enabler for engine downsizing and reduced fuel consumption and CO2 emissions. |
Variable valve actuation | Various | Some examples include: variable valve timing is an important measure to reduce cold start HCs. Variable valve lift enables throttleless operation and improved efficiency. Cylinder deactivation reduces part load pumping losses and improves efficiency. Variable valve timing enables Miller cycle operation for reduced pumping losses. |
Lean burn | Fuel consumption | Lean burn can reduce pumping losses, heat transfer and improve working fluid characteristics to provide higher efficiency. Introduces the need for expensive NOx aftertreatment technologies. |
Combustion | Fuel consumption | Advanced combustion concepts can improve efficiency through faster combustion and lower heat losses. |
EGR | At one time used to limit NOx emissions. Modern approaches focus mainly on reducing fuel consumption. | In SI engines, EGR is an alternative to fuel enrichment at high loads to reduce knock propensity and lower exhaust temperature at high power. At part load conditions, it can reduce pumping losses. |
Measurement of exhaust emission:
Some of the commonly used methods are:
1. Flame Ionization Detector (FID)
2. Spectroscopic Analyzer
3. Gas Chromatography
Non-Dispersive Infra-red (NDIR) Analyzer:
[A] + [b] → [◊] → [products] + light
[A], [b]: reactants
[◊]: Excited intermediate.
For example, if [A] is luminol and [B] is hydrogen peroxide in the presence of a suitable catalyst we have:
Luminol + H2O2 →3-APA[◊] →3-APA + light
Where:
Smoke meter:
The stages are typically referred to as Euro 1, Euro 2, Euro 3, Euro 4 and Euro 5 for Light Duty Vehicle standards.
The corresponding series of standards for Heavy Duty Vehicles use Roman, rather than Arabic numerals (Euro I, Euro II, etc.) The following is a summary list of the standards, when they come into force, what they apply to, and which EU directives provide the definition of the standard.
Bharat Stage Emission Standards Bharat stage emission standards are emission standards instituted by the Government of India to regulate the output of air pollutants from internal combustion engine equipment, including motor vehicles. The standards and the timeline for implementation are set by the Central Pollution Control Board under the Ministry of Environment & Forests.
The roadmap for implementation of the Bharat Stage norms were laid out till 2010. The policy also created guidelines for auto fuels, reduction of pollution from older vehicles and R&D for air quality data creation and health administration.
The standards, based on European regulations were first introduced in 2000. Progressively stringent norms have been rolled out since then. All new vehicles manufactured after the implementation of the norms have to be compliant with the regulations. Since October 2010, Bharat stage III norms have been enforced across the country. In 13 major cities, Bharat stage IV emission norms are in place since April 2010.
The phasing out of 2 stroke engines for two wheelers, the stoppage of production of Maruti 800 & introduction of electronic controls have been due to the regulations related to vehicular emissions.
While the norms help in bringing down pollution levels, it invariably results in increased vehicle cost due to the improved technology & higher fuel prices. However, this increase in private cost is offset by savings in health costs for the public, as there is lesser amount of disease-causing particulate matter and pollution in the air.
Emission Norms for Passenger cars
Norms | CO (g/Km) | HC + NOx (g/km) |
1991 Norms | 14.3 – 27.1 | 2.0 (Only HC) |
1996 Norms | 8.68 – 12.40 | 3.00 – 4.36 |
1998 Norms | 4.34 – 6.20 | 1.50 – 2.18 |
Indian Stage 2000 Norms | 2.72 | 0.97 |
Bharat Stage – (II) | 2.2 | 0.5 |
Bharat Stage – (III) | 2.3 | 0.35 (combined) |
Bharat Stage – (IV) | 1.0 | 0.18 (combined) |
Emission norms for Heavy Diesel vehicles
Norms | CO (g/Kmhr) | NOx (g/Kmhr) | PM (g/Kwhr) | HC (g/Kmhr) |
1991 Norms | 14 | 18 | - | 3.5 |
1996 Norms | 11.2 | 14.4 | - | 2.4 |
Indian Stage 2000 Norms | 4.5 | 8.0 | 0.36 | 1.1 |
Bharat Stage – (II) | 4.0 | 7.0 | 0.15 | 1.1 |
Bharat Stage – (III) | 2.1 | 5.0 | 0.10 | 1.6 |
Bharat Stage – (IV) | 1.5 | 3.5 | 0.02 | 0.96 |
Emission Norms for 2/3-wheeler
Norms | CO (g/Kmhr) | HC + NOx (g/Km) |
1991 Norms | 12 – 30 | 5 – 10 (only HC) |
1996 Norms | 4.5 | 3.6 |
Indian Stage 2000 Norms | 2.0 | 2.0 |
Bharat Stage – (II) | 1.6 | 1.5 |
Bharat Stage – (III) | 1.0 | 1.0 |
Reference:
1. Arora C. P., “Refrigeration and Air Conditioning”, Tata McGraw-Hill
2. V. Ganesan, “Internal Combustion Engines”, Tata McGraw-Hill
3. M. L. Mathur and R.P. Sharma, “A course in Internal combustion engines”, Dhanpat Rai & Co.
