4.1 Engine Testing Engine Testing Procedure | unit 4 ic engine testing and emission

IC Engine Testing and Emission

4.1 Engine Testing: Engine Testing Procedure

The basic task in the design and development of engines is to reduce the cost and improve the efficiency and power output.

In order to achieve the above task, the ‘development engineer’ has to compare the engine developed with other engines in terms of its output and efficiency. Towards this end he has to test the engine and make measurements of relevant parameters that reflect the performance of the engine.

I.C. engine generally operates within a useful range of speed. Some engines are made to run at fixed speed by means of speed governor, which is its rated speed. The performance of the engine depends on the inter-relationship between the power developed, speed and the specific fuel consumption at each operating condition within the useful range of speed and load.

The following factors are to be considered in evaluating the performance of an engine:

Maximum power or torque available at each speed within the useful range of speed. The range of power output at constant speed for stable operation of the engine. The different speeds should be related at equal intervals within the useful speed range.

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.

4.2 Measurement of Indicated Power

The indicated power of an I.C engine is the total power developed within the cylinder in one complete cycle neglecting any losses. It is the sum total of the brake power and the friction power of an 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.

4.3 Brake power

Brake Power (bp):

Delivered by the engine.

The power, bp, is usually measured by attaching a power absorption device to the drive-shaft of the engine. Such a device sets up measurable forces counteracting the forces delivered by the engine and the determined value of these measured forces is indicative of the forces being delivered.

Observed brake power is given by the formula:

Brake Power, bp = (W−S) x 2𝝅( 𝑫+𝒅𝟐 )xN 𝟔𝟎𝒙𝟏𝟎𝟎𝟎 kW

4.4 Fuel consumption

Brake specific fuel consumption (BSFC) is a parameter that reflects the efficiency of a combustion engine which burns fuel and produces rotational power (at the shaft or crankshaft).

4.5 Measurement of friction power by Willan’s Line Method and Morse Test

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:

Willan’s line method is only used in the compression ignition (C.I) engine. It is not applicable to S.I engine.

The friction power given by this method is approximate.

Friction power changes while an increase in engine speed. That’s why the engine should run at a constant speed throughout the Willan’s line test.

Measurement of friction power by Morse test:

Morse test is a method to measure the frictional power of a multicylinder SI engine.

Morse Test – This test carried out on multi cylinder I.C. engine. In this test, first engine is allowed to run at constant speed and brake power of engine is measured when all cylinders are working and developing indicated power. (Considering Four cylinders).

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.

4.6 Calculation of mean effective pressure,

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:

4.7 Various Efficiencies

Brake thermal efficiency:

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

Indicated thermal efficiency:

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:

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:

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.

4.8 Specific Fuel Consumption

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.

4.9 Heat Balance Sheet of IC Engines and performance Characteristic curves

Heat balance sheet

Heat balance sheet is a tabulated format in which complete record of heat supplied and heat rejected by an i.c.engine during a certain time duration (say 1 minute or 1 hour) is entered.

The following value are required to complete heat balance sheet of of I.C. engine.

Heat input is the heat produced due to combustion of the fuel

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

heat equivalent to B.P.

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

The mass of cooling water circulated through the cylinder jackets and its inlet and outlet temperatures are measured in order to find the heat reject to the cooling water by the engine cylinder

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)

Then heat reject to the cooling water

mw Cpw (Tw0 - Tw1) (in KJ/min)

c. Heat carried away by exhaust gases

The mass of exhaust gases may be obtained by adding together the mass of fuel and air supplied.

The mass of air supplied maybe measured by an orifice or it may be calculated by the exhaust gas analyzer

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 CpegT in KJ/min

= meg Cpeg(Teg – Ta)

Where Teg = temperature of exhaust gases

Ta = atmospheric room temperature

d. Unaccounted heat

There may be some loss of heat due to friction leakage, radiation etc which cannot be determined experimentally.

In order to complete does heat balance sheet this loss is obtained by subtracting the heat absorbed in B.P., cooling water and exhaust gases from the heat supplied by fuel.

Heat balance sheet on minute basis is present as below

Heat input	KJ/min	%	Heat output	KJ/min	%
Heat supplied by fuel		100%	Heat equivalent to B.P.
			b. Heat rejected to cooling water
			c. Heat carried away by exhaust gases
			d. Unaccounted heat

Necessity of heat balance sheet

Heat balance sheet gives the record of heat supplied by combination of fuel and heat utilized in various ways.

Heat balance sheet give the necessary information about the performance of engine.

Heat balance sheet gives the approximate number of unaccounted losses, which included friction losses, radiation losses from various part of the engine and heat lost due to incomplete combustion.

Heat balance sheet give us an idea about the amount of energy wasted

due to several reasons and allows to think of the method to reduce the heat energy losses so incurred.

4.10 Emission & Control: Introduction to Indian Driving Cycle (IDC)

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.

4.11 European Driving Cycle (EDC)

The New European Driving Cycle (NEDC) is a driving cycle, designed to assess the emission levels of car engines and fuel economy in passenger cars (which excludes light trucks and commercial vehicles).

It is also referred to as MVEG cycle (Motor Vehicle Emissions Group).

The cycle must be performed on a cold vehicle at 20–30 °C (typically run at 25 °C).

The cycles may be performed on a flat road, in the absence of wind. However, to improve repeatability, they are generally performed on a roller test bench. This type of bench is equipped with an electrical machine to emulate resistance due to aerodynamic drag and vehicle mass (inertia).

4.12 SI and CI Engines Emission and controlling methods

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.

4.13 Methods to measure emission such as (Non-Dispersive Infrared Red (NDIR)

Measurement of exhaust emission:

Substances emitted to atmosphere from any opening downstream of exhaust port. For a complete combustion of stoichiometric mixture, the emission only contains CO2 & H2O. (Rare case).

Mostly exhaust contains CO, UBHC & NOx.

Numerous devices have been developed to measure exhaust emissions.

Some of the commonly used methods are:

1. Flame Ionization Detector (FID)

2. Spectroscopic Analyzer

3. Gas Chromatography

Non-Dispersive Infra-red (NDIR) Analyzer:

The exhaust gas being measured is used to detect itself.

Done by selective absorption.

Infra-red energy of particular wavelength or frequency is peculiar to a certain gas.

The gas will absorb the IR energy of this wavelength and transmit IR energy of other wavelengths.

So, energy absorbed at this wavelength is an indication of concentration of CO in exhaust gas.

Consists of 2 IR sources, interrupted simultaneously by an optical chopper. Radiation from the sources pass in parallel paths through a reference cell and a sample cell to a common detector in the opposite side.

Sample cell contains sample to be analyzed.

This compound is not present in the reference cell.

It usually contains inert gas, usually Nitrogen, which doesn’t absorb IR energy for wavelength corresponding to compound to be measured.

A closed container filled only with the compound to be measured works as detector.

4.14 Flame Ionization Detector (FID)

It has flame ionization detector burner.

A hydrogen-air flame contains negligible amount of ions.

But if organic compounds such as HC are introduced, large number of ions are produced.

If a polarized voltage is applied across the burner jet and adjacent collector, an ion migration will produce a current proportional to no. of ions and thus to the HC concentration in the flame.

The output of FID depends on no of C atoms passing through the flame in a unit time.

FID output is usually referred to a std HC, usually ppm of normal heptane

Presence of CO, CO2, NOx, water & N in exhaust have no effect on FID reading.

FID analyzer is a rapid, continuous and accurate method of measuring HC in exhaust gas.

4.15 Chemiluminescent Analyzer, Smoke meter

Chemiluminescent immunoassays are variations of the standard ELISA where an enzyme converts a substrate to a reaction product that emits photons of light instead of developing a visible color.

The chemiluminescent substance is excited by the oxidation and catalysis forming intermediates.

When the excited intermediates return back to their stable ground state, a photon is released, which is detected by the luminescent signal instrument.

Emission of light with limited emission of heat (luminescence), as the result of a chemical reaction.

[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:

3-APA is 3-aminophthalate

3-APA [◊] is the excited state producing light as it decays to a lower energy level.

Chemiluminescence differs from fluorescence or phosphorescence in that the electronic excited state is the product of a chemical reaction rather than of the absorption of a photon.

It is the antithesis of a photochemical reaction, in which light is used to drive an endothermic chemical reaction.

Light is generated from a chemically exothermic reaction.

Smoke meter:

For measuring smoke density Smoke Meters are generally used.

Smoke meters, also referred to as opacity meters, detect and measure the amount of light blocked in smoke emitted by diesel engines from cars, trucks, ships, buses, motorcycles, locomotives and large stacks from industrial operations.

The smoke meter readout displays the smoke density giving a measure of the efficiency of combustion. This makes the smoke meter an excellent diagnostic tool to ensure proper maintenance of diesel engines for improved fuel economy and protection of the environment.

4.16 Euro Norms and Bharat Stage Norms

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.

Euro 1 (1993): – For passenger cars - 91/441/EEC. – Also, for passenger cars and light trucks - 93/59/EEC.

Euro 2 (1996) for passenger cars - 94/12/EC (& 96/69/EC) – For motorcycle - 2002/51/EC (row A) - 2006/120/EC.

Euro 3 (2000) for any vehicle - 98/69/EC – For motorcycle - 2002/51/EC (row B) - 2006/120/EC.

Euro 4 (2005) for any vehicle - 98/69/EC (& 2002/80/EC).

Euro 5 (2008/9) and Euro 6 (2014) for light passenger and commercial vehicles - 715/2007/EC.

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.

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