Otto motorTesting of an internal combustion engine

Exhaust gas composition

Three-way catalytic converter

Motor energy balance

1

Internal combustion engines – 1.

• An Otto motor is a four-stroke (also known as four cycle), spark-ignition engine.

• It is an internal combustion (IC) engine in which the piston completesfour separate strokes while turning a crankshaft.

• A stroke refers to the full travel of the piston along the cylinder, in either direction.

2

The Otto cycle

3

4

The four-stroke Otto motor1. Intake: This stroke of the piston begins at top dead center (TDC)

and ends at bottom dead center (BDC). In this stroke the intake valve is open, while the piston pulls an air-fuel mixture into the cylinder by producing vacuum pressure into the cylinder through its downward motion.

2. Compression: This stroke begins at BDC (at the end of the suction stroke). Ends at TDC. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke. Both the intake and exhaust valves are closed during this stage.

3. Combustion: This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a 360⁰revolution. While the piston is at TDC (end of the compression stroke) the compressed air-fuel mixture is ignited by a spark plug (in a gasoline engine) or by heat generated by high compression (diesel engines), forcefully returning the piston to BDC. This stroke produces mechanical work from the engine to turn the crankshaft.

4. Exhaust: During the exhaust stroke, the piston once again returns from BDC to TDC while the exhaust valve is open. This action expels the hot gas mixture, through the exhaust valve.

5

Internal combustion engines – 2.

• The Diesel motor (also known as a compression-ignition or CI engine) is an internal combustion engine in which ignition of the fuel is initiated by the high temperature which a gas achieves when greatly compressed (adiabatic compression).

• This contrasts with spark-ignition engines such as a gasoline engine or gas engine (using a gaseous fuel instead of gasoline), which use a spark plug to ignite an air-fuel mixture.

• In the case of a Diesel engine it uses glow plugs.

6

The Diesel cycle

7

4-stroke compression-ignition (Diesel) engine cycle

8

Chain of losses in spark ingnited petrol engine

11

Heat of combustion• The heat of combustion is the total energy released

as heat when a substance undergoes complete combustion with oxygen under standard conditions.

• The chemical reaction is typically an organic molecule (hydrocarbon) reacting with oxygen to form CO2 and H2O and release heat.

• The heating value (energy value or calorific value) of a substance, usually a fuel, is the amount of heatreleased during the combustion of a specified amount of that substance.

• The heat of combustion is conventionally measured with a calorimeter.

12

Higher and Lower Heating Value• The Higher Heating Value (HHV) (or gross energy or

upper heating value or gross calorific value (GCV) or higher calorific value (HCV)) is determined by bringing all the products of combustion back to the original pre-combustion temperature, and condensing any vaporproduced.

• The Lower Heating Value (LHV) (net calorific value(NCV) or lower calorific value (LCV)) is determined by subtracting the heat of vaporization of the water vapor from the higher heating value. This treats any H2O formed as a vapor. The energy required to vaporize the water therefore is not released as heat.

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Relation between heating values• The difference between the two heating values depends on the

chemical composition of the fuel.• In the case of pure carbon or carbon monoxide, the two heating

values are almost identical, the difference being the sensible heat content of carbon dioxide between 150 °C and 25 °C.

• For hydrogen the difference is much more significant as it includes the sensible heat of water vapor between 150 °C and 100 °C, the latent heat of condensation at 100 °C, and the sensible heat of the condensed water between 100 °C and 25 °C. The higher heating value of hydrogen is 18.2% above its lower heating value (142 MJ/kg vs. 120 MJ/kg).

• For hydrocarbons the difference depends on the hydrogen content of the fuel. For gasoline and diesel the higher heating value exceeds the lower heating value by about 10% and 7% respectively, and for natural gas about 11%.

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Higher (HHV) and lower (LHV) heating values

of some common fuels

Fuel HHV MJ/kg HHV kJ/mol LHV MJ/kg

Hydrogen 141.80 286 119.96

Methane 55.50 889 50.00

Ethane 51.90 1,560 47.80

Propane 50.35 2,220 46.35

Butane 49.50 2,877 45.75

Pentane 48.60 3,507 45.35

Paraffin wax 46.00 41.50

Kerosene 46.20 43.00

Diesel 44.80 43.4

Coal (Anthracite) 32.50

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Heat of combustion for some common fuels (HHV)

Fuel kJ/g kcal/g

Hydrogen 141.9 33.9

Gasoline 47.0 11.3

Diesel 45.0 10.7

Ethanol 29.7 7.1

Propane 49.9 11.9

Butane 49.2 11.8

Wood 15.0 3.6

Coal (Lignite) 15.0 4.4

Coal

(Anthracite)36 7.8

Natural Gas 54.0 13.0

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Energy content of fuel• Gasoline or petrol is a fuel, derived from petroleum

crude oil, for use in spark-ignited internal combustion engines.

• Gasoline is used primarily as fuel for the internal combustion engines in automotive vehicles as well in some small airplanes.

• Conventional gasoline is mostly a blended mixture of more than 200 different hydrocarbon liquids ranging from those containing 4 carbon atoms to those containing 11 or 12 carbon atoms.

• Gasoline has an initial boiling point at atmospheric pressure of about 35 °C and a final boiling point of about 220 °C.

17

Energy content• Energy is obtained from the combustion of gasoline by

the conversion of a hydrocarbon to CO2 and H2O.

• The combustion of octane follows this reaction:

2 C8H18 + 25 O2 → 16 CO2 + 18 H2O

• Gasoline contains about 42.4 MJ/kg energy, quoting the

Lower Heating Value (LHV).

• Molecular weights of the above reagents are

C8H18 114, O2 32, CO2 44, H2O 18;

therefore 1 kg of fuel reacts with 3.51 kg of oxygen to

produce 3.09 kg of carbon dioxide and 1.42 kg of water.

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Engine efficiency

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Typical distillation curve• Starting and Vapor Lock

Protection (10 - 20 - 30% temp.)

Starting ability is controlled by the Reid Vapor Pressure and the front-end

of the distillation curve.

• Engine Warm-Up andAcceleration (related to the 50%

and 90% temp.) Advantage of a low

90% evaporated temperature is the reduced tendency for crankcase dilution.

• Fuel Economy (related to 90% to

end point temp.) The higher boiling components have higher energy contents per liter.

20Gasoline volatility is adjusted seasonally

Gasoline requrementsand properties

In order to maintain top road performance and best fuel economy gasoline must be formulated and blended to provide:

– Good mileage under all driving conditions

– Fast starts

– Rapid warm-up

– Smooth performance

– Minimum engine maintenance

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Performance characteristics of gasolines

• The three major factors:

– Volatility

– Anti-knock quality

– Deposit control

1. Volatility. This is a measure of the tendency of a gasoline to change from

a liquid to a vapour. Gasoline volatility is characterised by Reid VapourPressure.

2. Anti-Knock Quality (Octane Number). As the compression ratio

goes up, knocking tendency increases and the anti-knock value of the fuel becomes critical. The octane number of a gasoline is a measure of its anti-knock quality or ability to resist detonation during combustion.

3. Deposit control. Oxidation inhibitors are added to help in controlling

gum and deposit formation.

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Calculations -1.• Calculation of calorific value (Lower Heating Value, LHV):

LHV = HHV – RR = evaporation heat of water (Regnault heat)

If the hydrogen content of the fuel is mH [kg hydrogen/kg fuel]

then burning of 1 kg fuel ➔ 9 mH [ kg ] water.

• R = Lp 9 mH

where Lp is the heat of vaporization ~ 2500 kJ/kg, ( 0⁰C and 101.325 kPa )

• Excess air calculation:

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0L

L=

L = actual intake air

L0 = theoretical air quantity

The engineering unit of L and L0 is the same [Nm3 air/kg fuel, Nm3 air/hour]

both must be expressed in the same volume or mass units.

1

1

Lean mixture

Rich mixture

Calculations -2.

• Residual O2 concentration of flue gas:(Calculation from the O2 or CO2 concentration of flue gas.)

24

gasflueofvolumedry

volumeOO 2

2 =

( )

( )00

02

21.0

LLV

LLO

dry −+

−=

volumegasfluedryltheoreticaV dry =0

0

0

2

2

%21

%1

L

V

O

O dry

−

+=

Applying substitution:

Calculations -3.• The theoretical air demand, dry and wet flue gas

volume is calculated from the composition of fuel.

• Assume that 1 kg of fuel is composed bymC kg carbon, mH kg hydrogen, mO kg oxygen

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Note: Volume of 32 kg oxygen is 22.41 Nm3,

therefore mO kg oxygen is 22.41 x mO / 32 Nm3

Calculations -4.

• Theoretical oxygen demand:

• Nitrogen enters together with oxygen to combustion

• Air demand is the sum of O2 and N2 volume

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fuelkg

oxygenNmmmmdemandO OHC

3

232412

41.22

−+=

fuelkg

nitrogenNmmmmvolumeN OHC

3

232412

41.2221

79

−+=

fuelkg

aircombustionNmmmmL OHC

3

032412

41.2221

100

−+=

Calculations -5.Theoretical volume of dry and wet flue gas (V0

dry , V0wet)

• Theoretical volume of dry flue gas: (components: N2 (entered together with O2), and CO2 )

• Theoretical volume of wet flue gas: (components: N2 (entered together with O2), CO2 , H2O steam)

27

fuelkg

fluegasdryNmmmmV OHCdry

3

032

79.0

4

79.0

1241.22

21

100

−

+=

fuelkg

fluegaswetNmmmmV OHCwet

3

032

79.0

4

21.1

1241.22

21

100

−

+=

Testing the Otto motor• Purpose of this test is to investigate the

– Exhaust gas composition

– Efficiency of three-way catalytic converter

– Energy balance of the Otto motor

• For the purpose of this test the fuel/air ratio in the mixture can be controlled.

• Flow rate of the carburetted fuel is also controlled.

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Effect of air/fuel ratio• During the test we will examine:

– the uncleaned exhaust gas compositions

– the gas composition after three-way catalytic converter at different air/fuel ratios

– calculate the cleaning efficiency.

• Mass flow of carburetor intake air is constantbecause of the

– constant displacement,

– air pressure,

– temperature,

– engine speed.

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Adjustment of the air/fuel ratio

• In the carbureter housing the float’s needle valve canbe moved up and down.

• With help of this action the float position in the housing (float position, mm h), the hydrostatic pressure can be varied.

• If the floating position is increased the volumetric flow of gasoline increases linearly in the fuel/air mix.

• The air ratio is reduced, therefore the intake mixture will be more and more rich.

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The catalytic converter• The catalytic converter is placed immediately after the engine

in the exhaust pipe. The gas sampling is before and after the catalyser and the connections of thermocouples also.

• Technical details:Type: single bed, three-wayThe active substance: Pt, Pd, RhSize: 100 x 100 x 130 mm

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Specific cell density: 62 /cm2

Specific internal surface: 18.0 m2 /cm3

Total inner surface: 15 080 m2

Internals of ceramic body

The measurement• During the test the following parameters are constant:

– compression ratio, (ε)

– air temperature, (tair )

– revolution number (N)

– spark advance (α)

• While the engine is running: carburetor float position (h)can be adjusted. At the same time this will modify λ (excess air) also.

• In each float position we have to wait until the stationary condition (steady state) is achieved.

• The composition and temperature of exhaust gases arerecorded before and after the catalytic converter.

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Effect of the load

• During the practice an Otto-motor powered electrical generator (Honda) tested under various electrical loads.

• Investigate the exhaust gas composition:

– uncleaned composition before the catalyzer

– the purified composition at the output of the three-way catalytic converter

• Calculate and record the energy balance of the Otto motor.

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The test equipment• The Honda engine is a two-cylinder, 359 cm3 displacement,

four-stroke, liquid-cooled gasoline engine that drives an electric generator running on a common shaft. (The unit is designed to provide electricity in places where there is no network or power failure is not allowed.)

• The engine speed is constant (3000 rpm), because of the frequency requirement.

• The engine compression ratio is 8.5: 1.

• The engine’s excess heat in a fan-cooled heat exchanger cools back (water meters measure volumetric flow of coolant) , but the engine itself is also cooled by a fan, placed on the common shaft.

34

System components• The volume of intake fuel delivered by the engine’s fuel pump

can be followed by a graduated metering glass.

• The exhaust gas is passing through a three-way catalytic converter and the exhaust silencer. Before and after the catalytic converter gas samples are taken to the gas analyzer.

• Resistance thermometers are used to measure:– Coolant temperature entering and leaving heat exchanger,

– Exhaust gas temperature entering and leaving the catalytic converter.

• Output of the electric generator is connected to two, 1 and 2 kW oil radiator. The actual output power and the generator performance can be measured.

• The tail pipe (outlet) is connected to a suction fan and the exhaust gas leave the room through the chimney.

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The analyzers• Composition of the exhaust gases is

measured Bosch Emission Analyzer device (BEA). The device is suitable for petrol and diesel cars pollutant emissions, and other motor parameters (speed, oil temperature, closing angle etc) to investigate.

• The analyzer module measures the CO2, CO, HC, O2 and NOX content, and calculates air/fuel ratio.

• Gas components are measured by electrochemical cells or IR absorption cells.

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Operation of the Analyzer• The electrochemical cells (galvanic cells) using

component selective electrochemical reactions for the given gas.

– The produced electric signal is proportional with the concentration of the selected component.

• The operation of the IR-cell is based on the priciple: the hetero-atomic gases in the infrared light at a certain wavelength range, are selectively absorb radiation.

– The absorption rate is proportional to the concentration of the respective component.

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• We will investigate the engine output while the generator power output is:

1. Unloaded

2. Loaded in steps by 1, 2, 3 and 4 kW resistive loads

• Following variables are measured after reaching the steady state condition in each load steps:

– Composition of exhaust gas before and after the catalytic converter.

– Temperature of exhaust gas before and after the catalytic converter.

– Power output of the generator

– Fuel consumption of the engine

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The measurement

The 3-way catalytic converter

With the help of the catalyzer more

than 90% of the harmful exhaust gas

components are converted to more

„environmental friendly” components

like H2O, N2, CO2

Measured emissions:

a./ before catalyzer

b./ after catalyzer

c./ Voltage output of lamda sonde

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Evaluating the impact of air/fuel ratio

• At the highest excess air level (the lowest float position) the air/fuel ratio can be calculated from the O2 content engine exhaust gas as it is given in the theoretical introduction. (However, at other floating mounting positions not only the perfect combustion products are present, can only be applied more complicated formula.)

• At an air deficiency position, due to the short reaction time, oxygen also exists, but the formula will result in λ > 1 also.

• At other float positions λ can be calculated:

• L0 is proportional with the fuel consumption: where A2 = constant [ kg air / dm3 fuel ]

Vb = fuel consumption [ dm3 fuel / h]

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L = actual intake air [ kg/h ]

L0 = theoretical air demand [ kg/h ]

Evaluating the impact of air/fuel ratio

• Earlier fuel cunsumption tests proved that the Vb in this engine is a linear function of the float level.

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where A3 = construction constant

where

If λ = 1, then A = h, therefore A is the actual float position in [mm]

The numeric value of A can be calculated from the λ, and based

on the measured O2 concentration and the float level h.

Calculation of other λ values are

based on the actual float level [mm]

Calculation of the conversion

• Conversion efficiency is calculated with the following formula (for all components to be reduced ):

Note:

1. Measurement accuracy for O2, CO, and NO is good,

2. The HC and NO2 quantities are very small,therefore may be measured with a large error.

42

%100)(=

catalyzerbeforeionconcentratinitial

catalyzeronreductionionconcentrat

Evaluations - effect of the load

• Energy balance calculation include at each load steps, – Engine intake heat (fuel energy) per unit time,

– Three heat output during the measurement period.

• The measured outputs:– Electric power output of the generator

– Heat output of coolant (thermal power loss)

– Flue gas heat output (thermal power loss)

• The heat input per unit time (at each load steps) equals withthe product of fuel’s mass flow rate and the calorific value

43

density of fuel

volumetric flowrate

F = calorific value

Heat output of coolant (loss)

• The cooling water carry away heat. This thermal loss can be calculated as follows:

44

coolantcoolantcoolantcoolantcoolantcoolantcoolantcoolant tcVtcmQ ==

coolantofincreaseetemperaturtcoolant =

coolantofheatspecifickgK

kJccoolant 2.4=

coolantcoolantcoolantcoolant

coolant tcV

Q −

=

12

readingsbetweentimeelapsed=− 12 3

1000m

kgcoolant =

meterflowcoolantonincreaseVcoolant =

Flue gas heat output (loss)

• The flue gas carry away heat.

• The thermal loss (power loss) can be calculated as follows:

45

fgfgfgfuelfgfgfggasflue tcVmtcVQ ==

( ) ( )10000 −+=−+ i

wet

i

wet

fg LVLLVV Excess air

wet

fg VV 0Air

deficiency

gasflueofheatspecificc fg =

( ) measuredetemperaturttt aircatalyzerbeforefg ,−=

The electric power• The electric power is directly measured on the load,

or calculated.

• The measured electrical power is the ratio of electrical work (Welectr) and the elapsed time (τelectr)

46

electric

electricelectric

WQ

=

Conclusions• Useful conclusions can be made if you calculate the

heat output and heat input (% share) at all fuel flowrates:

• The sum of these values naturally does not give 100 % because not all heat output is measured during the test.

• Unknowns are the following (not calculated losses): – heat radiated by the engine to the surrounding environment,

– power loss of the generator,

– heat released by the conduits of cooling fluid

– unburned loss, which occurs due to incomplete combustion.

47

100=fuel

coolantcoolant

Q

Q 100=

fuel

electricelectric

Q

Q 100=

fuel

fg

fgQ

Q

Review questions

• What is the catalysis, heterogeneous catalysis?

• What is the definition and calculation of l?

• What are the components of exhaust gas of an Otto motor?

• What is the concentration range of the components in the exhaust gas?

• Which components are generating air pollution?

• What is the definition of combustion heat and calorific value?

• What are the chemical reactions on the three-way catalytic converter?

• What are the parameters which will affect the conversion?

• What heat outputs are measured for the energy balance calculation?

48

Questions after the calculations

• What are the most important properties of gasoline?

• How the gasoline for spark ignition engines is produced?

• What is the value of λ, if octane-air mix is burning, and 2% the oxygen concentration measured in the dry flue gas ?

• How the composition of exhaust gas will change as a function of λ ?

• How does the theoretical conversion ratio will change as a function of excess air?

• What is the structure of three-way catalyst and what are the active ingredients?

• Which parameters and how they affect the value of the conversion?

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Thank you for your attention...

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