internal combustion engine fundamentals are discussed

NATIONAL INSTITUTE OF NATIONAL INSTITUTE OF TECHNICAL TEACHERS TECHNICAL TEACHERS

TRAINING AND RESEARCH TRAINING AND RESEARCH CHANDIGARH CHANDIGARH

112/20/14

Vehicle ownership is still growing worldwide

By 2020– 15% vehicle ownership – 1.1 billion vehicles– Circle the earth 125 times

Purpose of an engine

Converts the heat of burning fuel into useful energy

Internal Combustion Engines

When expressed as a percentage, the thermal efficiency must be between 0% and 100%. Due to inefficiencies such as friction, heat loss, and other factors, thermal engines' efficiencies are typically much less than 100%. For example, a typical gasoline automobile engine operates at around 25% efficiency. The largest diesel engine in the world peaks at 51.7%.

Basic Terminology

•Bore & Stroke

•Engine Displacement

•Compression Ratio

•Power

•Torque

Premixed vs. Non-premixed Charge Engines

Flame front Fuel spray flame

Premixed charge (gasoline)

Non-premixed charge (Diesel)

Spark plug Fuel injector

Fuel + air mixture Air only

Internal Combustion Engines – Carnot cycle

The Ideal Air Standard Otto Cycle

The basic requirements of an engine are to provide:• High power output

• High thermal efficiency and low specific fuel consumption

• Smooth engine operation

• Reduced exhaust pollutants.

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Is it Really A Great Achievement

• In 1893, the Benz Velo became the world's first inexpensive, mass-produced car.

• 0.7 hp and 958cc !!!

• The Mercedes 35 HP was a radical early car model designed in 1901.

• Engine volume: 5,918CC.

• A break through in Auto Sports ran a speed of ~35KMPH.

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Higher Power Output

1.High Volumetric Efficiency

2.High Compression Ratio

3.No Excess Air

4.Complete Utilization of Air

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..\AEM Performance Electronics – What is Volumetric Efficiency (VE).mp4

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• Volumetric efficiency (ηv) = (mass of air actually drawn into cylinder) / (mass of air that ideally could be drawn into cylinder)

where ρair is at ambient = Pambient/RTambient and R - 287 J/kgK for air• Volumetric efficiency indicates how well the engine “breathes” -

what lowers ηv below 100%?– Pressure drops in intake system (e.g. throttling) & intake

valves– Temperature rise due to heating of air

– Volume occupied by fuel– Non-ideal valve timing

– “Choking” (air flow reaching speed of sound) in part of intake system having smallest area

Volumetric Efficiency

nNVdairv /

(measured) mair

ρη

≡

Engines

Different arrangement of valve and camshaft.

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• Engine performance is specified in both in terms of power and engine torque - which is

more important?– Wheel torque = engine torque x gear ratio

tells you whether you can climb the hill

Power and Torque

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– Power tells you how fast you can climb the hill– Torque can be increased by transmission (e.g.

2:1 gear ratio ideally multiplies torque by 2) Power can’t be increased by transmission; in

fact because of friction and other losses, power will decrease in transmission

– Power tells how fast you can accelerate or how fast you can climb a hill, but power to torque

ratio ~ N tells you what gear ratios you’ll need to do the job

There is a maximum in the brake power versus engine speed called the rated

brake power.

At higher speeds brake power decreases as friction power becomes significant compared

to the indicated power

There is a maximum in the torque versus speed called maximum brake torque (MBT).

Brake torque drops off: • at lower speeds do to heat losses

• at higher speeds it becomes more difficult to ingest a full charge of air.

Max brake torque

1 kW = 1.341 hp

Rated brake power

Power and Torque versus Engine Speed

I.C. Engines Laboratory

December 20, 2014 I.C. Engines Laboratory Slide 29

Effect of Fuel-Air Ratio on Power Output of CI Engine

HIGH THERMAL EFFICIENCY

• High compression ratio

• A small heat loss during combustion. This is achieved by having a compact Combustion chamber which provides small surface – volume ratio.

• Compact combustion chamber is reduced flame travel

• Good scavenging of the exhaust gases.

Direct Injection vs. Indirect Injection

SMOOTH ENGINE OPERATION

• Moderate rate of pressure rise during combustion.

• Absence of detonation

• Short distance of flame travel

• Proper location of the spark plug and exhaust valve.

• Satisfactory cooling of the spark plug points

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Engines

It provides the means of ignition when the gasoline engine’s piston is at the end of compression stroke, close to Top Dead Center(TDC)

Spark Plug

The difference between a "hot" and a "cold" sparkplug is that the ceramic tipis longer on the hotter plug.

Knock

As the flame propagates away from the spark plug the pressure and temperature of the unburned gas increases.

Under certain conditions the end-gas can autoignite and burn very rapidly producing a shock wave

The end-gas autoignites after a certain induction time which is dictated by the chemical kinetics of the fuel-air mixture.

If the flame burns all the fresh gas before autoignition in the end-gas can occur then knock is avoided.

Therefore knock is a potential problem when the burn time is long!

shockP,T

time time

P,Tend-gas

flame

Fuel Requirements

• Gasoline is a mixture of hydrocarbons (with 4 to approximately 12 carbon atoms) ,SIT 450 oC

• Diesel fuel is a mixture of higher molar mass hydrocarbons (typically 12 to 22 carbon atoms), SIT 200 oC.

• Fuels for spark ignition engines should vaporize readily and be resistant to self-ignition, as indicated by a high octane rating.

• Fuels for compression ignition engines should self-ignite readily, as indicated by a high cetane number.

• Equivalence Ratio:

• Lambda is the ratio of the actual air-fuel ratio to the stoichiometric air-fuel ratio defined as

Methods of Quantifying Fuel and Air Content

of Combustible Mixtures

• If less air than the stoichiometric amount is used, the mixture is described as fuel rich.

• If excess air is used, the mixture is described as fuel lean.

• Fuel-Air Ratio (FAR): The fuel-air ratio, f, is given by

Octane number

Standard measure of the anti-knock

properties (i.e. the performance) of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating.

Cetane Number

CN is a measurement of the combustion quality of diesel fuel during compression

ignition.

Cetane Number

• Measures readiness of fuel to auto-ignite.• High cetane means the fuel ignite quickly• Most fuels have cetane numbers between 40

and 60.• ASTM requires a minimum cetane number of

40• Premium Diesel fuel typically has a cetane of

47

December 20, 2014Slide 47

Dr. J. M. MallikarjunaInternal Combustion Engines Laboratory, Indian Institute of Technology Madras, Chennai - 600036

Cetane

Ignition Delay: The period that occurs between the start of fuel injection and the start of combustion; the higher the cetane number, the shorter the ignition delay and the better the quality of combustion.

Cetane


Stages of Combustion in CI Engines

Type of Combustion Chambers for SI engines

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Reduced Exhaust Pollutants

Exhaust pollutants can be reduced by designing a combustion chamber that produces a faster burning rate of fuel

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12/20/14 Prof. M.P.Poonia, Director, NITTTR, Chandigarh

Emission sources in a gasoline fuelled car

Ref : http://nptel.iitm.ac.in/courses/112104033/2

Emission Sources in a Diesel Engine Powered Bus

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5 Major Pollutants :5 Major Pollutants :

1 . . ) Carbon Monoxide

2. ) Sulfur Dioxide

3. ) Nitrogen Dioxide

4. ) Part iculate Matter

5. ) Ground Level

Ozone

Hydrocarbons – Lung Cancer

Emission norms for passenger cars ( Petrol)

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Norms CO( g/km) HC+ NOx)(g/km)

1991Norms 14.3-27.1 2.0(Only HC)

1996 Norms 8.68-12.40 3.00-4.36

1998Norms 4.34-6.20 1.50-2.18

stage2000 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:

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Norms CO (g/kwhr)

HC(g/kwhr)

Nox(g/kwhr)

PM(g/kwhr)

1991 Norms 14 3.5 18 -

1996 Norms 11.2 2.4 14.4 -

stage 2000 Norms 4.5 1.1 8.0 0.36

Bharat stage-II 4.0 1.1 7.0 0.15

Bharat Stage-III 2.1 1.6 5.0 0.10

Bharat Stage-IV 1.5 0.96 3.5 0.02

• Who wants to go on a break

• Everyone!!!!

I.C. ENGINE TESTING

Measurement of Air Supply of an I.C. Engine:

Measurement of Airby Air Box Method.

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Indicated WorkGiven the cylinder pressure data over the operating cycle of the engine one can

calculate the work done by the gas on the piston.

The indicated work per cycle is ∫= PdVWi

CompressionW<0

PowerW>0

IntakeW>0

ExhaustW<0

WA > 0

WB < 0

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Indicated Mean Effective Pressure (Pim):

p-V diagram for an ideal four-stroke cycle engine

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internal combustion engine fundamentals are discussed

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