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Unit – 4

IC Engine Testing and Emission

Q1) What is the Purpose of Testing of an I.C. Engine.

A1)

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.

Q2) Explain the Measurement of friction power by Willan’s line method.

A2)

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.

Q3) Explain the measurement of Mean effective pressure.

A3)

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:

Q4) Explain the various types of efficiency.

Brake thermal efficiency

Indicated thermal efficiency

Mechanical efficiency

Volumetric Efficiency

A4)

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.

Q5) Explain the Flame Ionization Detector (FID).

A5)

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.

Q6) Explain the Chemiluminescent Analyzer.

A6)

Chemiluminescent Analyzer

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.

Q7) What do you understand by Heat balance sheet. Explain in detail.

A7)

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 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 besome 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 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

Q8) Explain the Measurement of friction power by Morse test.

A8)

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.

Q9) Define the following:

Brake Power (bp)

Brake specific fuel consumption

Indicated power

A9)

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) x N 𝟔𝟎𝒙𝟏𝟎𝟎𝟎 kW

Brake specific 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).

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.

Q10) Explain the Non-Dispersive Infra-red (NDIR) Analyzer.

A10)

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.

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