Report of Engine Cooling & Exhaust System

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FACULTY OF MECHANICAL AND MANUFACTURING ENGINEERING

AERONAUTICAL ENGINEERING TECHNOLOGY

(PROFESSIONAL PILOTING)

AMALAN KEJURUTERAAN II BDU28001

REPORT ENGINE COOLING & EXHAUST SYSTEM

Lectures:

EN. QAMARUL EZANI BIN KAMARUDIN

EN. MOHD FIKRI BIN MOHD MASROM

Group Members: AMAL IQMAL B. ADNAN AD110189

MOHAMAD FHAIZZUDDIN B. ABD KADIR AD110030

MOHAMAD IRFAN B. AZMI AD110169

MOHAMAD FAZLE B. MOHAMMED AD110201

MUHAMMAD ZAHIN B. NORIZAN AD110210

NIK MUHAMMAD HISHAMUDDIN B. NICK HAMASHOLDIN AD110140

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TABLE OF CONTENTS

No. Topics Pages

1. Introduction

3

2. Air Cooling System

3-5

3. Liquid Cooling System

6-10

4. Straight Stack Exhaust System

10-12

5. Collector Exhaust System

13-14

6. Exhaust System with Supercharger

15-18

7. References

19

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ENGINE COOLING & EXHAUST SYSTEMS

INTRODUCTION

Engine cooling is a system that capable to transfer heat from hot region to cold

region either by conduction or convection in order to cool down the engine. There are two

types of engine cooling which are air cooled and liquid cooled. While an exhaust system is

a system usually piping used to guide reaction exhaust gases away from a controlled

combustion inside an engine or stove. The entire system conveys burnt gases from the

engine and includes one or more exhaust pipes. Depending on the overall system design,

the exhaust gas may flow through one or more of cylinder head and exhaust manifold, a

turbocharger to increase engine power, a catalytic converter to reduce air pollution, a

muffler/silencer, to reduce noise.

AIRCRAFT ENGINE COOLING SYSTEMS

AIR COOLING

Function

The burning fuel within the cylinders produces intense heat, most of which is

expelled through the exhaust system. Much of the remaining heat must be removed to

prevent the engine from overheating. So air cooled system was installed in motor vehicle to

cools down the engine.

Basic Principle

Majority of aircraft piston engine cooling is done by air. Some of them are cooled by

liquid. Air cooling is accomplished by air flowing into the engine compartment through

openings in front of the engine cowling. Baffles route this air over fins attached to the engine

cylinders, and other parts of the engine, where the air absorbs the engine heat. Expulsion of

the hot air takes place through one or more openings in the lower, aft portion of the engine

cowling. The outside air enters the engine compartment through an inlet behind the

propeller hub. Baffles direct it to the hottest parts of the engine, primarily the cylinders,

which have fins that increase the area exposed to the airflow.

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Figure 1: Aircraft air cooled system

In air cooled engine, thin metal fins project from the outer surfaces of the walls and

heads of the engine cylinders. When air flows over the fins it absorbs excess heat from the

cylinders. Fins on the cylinder head are forged or cast as part of the head. Fins on the steel

cylinder barrel are machined from the cylinder barrel forging. Deflector baffles is made from

aluminum sheet, it will fastened around the cylinders direct the flow of air to obtain the

maximum cooling effects.

Figure 2: Cylinder with baffles for cooling.

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The air cooling system is less effective during ground operations, takeoffs, go-

around, and other periods of high-power, low-airspeed operation. Conversely, high-speed

descents provide excess air and can shock cool the engine, subjecting it to abrupt

temperature fluctuations.

Operating the engine at higher than its designed temperature can cause loss of

power, excessive oil consumption, and detonation. It will also lead to serious permanent

damage, such as scoring the cylinder walls, damaging the pistons and rings, and burning

and warping the valves. Monitoring the flight deck engine temperature instruments will aid in

avoiding high operating temperature.

Engine operating temperature can be controlled by the movable cowl flaps located

on the engine cowling. Cowl flaps are hinged covers that fit over the opening through which

the hot air is expelled. If the engine temperature is low, the cowl flaps can be closed, so that

it will increase engine temperature. If the engine temperature is high, the cowl flaps can be

open to permit a greater flow of air through the system, so that it will decrease the engine

temperature. But under normal operating conditions in aircraft not equipped with cowl flaps,

the engine temperature can be controlled by changing the airspeed or the power output of

the engine. High engine temperatures can be decreased by increasing the airspeed and/or

reducing the power. The oil temperature gauge gives an indirect and delayed indication of

rising engine temperature, but can be used for determining engine temperature if this is the

only means available.

Advantages and disadvantages

1. Advantage

i. Less expensive compare to liquid cooled system.

ii. More light-weight.

iii. More environment-friendly.

2. Disadvantage

i. Uneven and unreliable cooling based on airflow.

ii. Air-cooled engine that fail generally require a major overhaul.

iii. Their maintenance and repair tasks tend to be more frequent and more time-

consuming.

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LIQUID COOLING

There are few aircraft currently fitted with liquid-cooled engines, but liquid cooling is

used extensively in cars. In liquid-cooled engines, the cylinders and cylinder head are

double walled, or and a liquid is circulated through the jackets. Preventing overheating is

one function of the cooling system. It also helps the engine reach its best operating

temperature as soon as possible. Every engine has a temperature at which it operates best.

Below this temperature, ignition and combustion can be difficult. Most engine wear occurs

during this warm-up period and most pollution too.

The basic coolant use for liquid cooling system is water, but because of the lower

temperatures at altitude, the addition of an anti-freeze agent is essential with aero engines

and a mixture of 70% water and 30% ethylene glycol is normally used. The industry term for

the antifreeze mixture is engine coolant. Some antifreezes use no water at all, instead using

a liquid with different properties, such as propylene glycol or a combination of propylene

glycol and ethylene glycol. Most "air-cooled" engines use some liquid oil cooling, to maintain

acceptable temperatures for both critical engine parts and the oil itself. Most "liquid-cooled"

engines use some air cooling, with the intake stroke of air cooling the combustion chamber.

An exception is Wankel engines, where some parts of the combustion chamber are never

cooled by intake, requiring extra effort for successful operation.

Working principle

In this very basic liquid-cooling system, a coolant is stored in a radiator, and in the

engine. As the engine heats up, a natural circulation starts, as coolant rises through the

engine block by convection. It passes through the top hose, and into the radiator. Inside the

radiator, heat is removed from the coolant as it falls from the top to the bottom. When it

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reaches the bottom, it returns to the engine through the lower radiator hose. This process is

called thermo-siphon. It was common in older cars which had low-powered engines and

high, narrow radiators. In modern cars, the engines are more powerful, and radiators are

low and wide, and a there siphon process couldn’t move the coolant quickly enough.

Instead, a water pump forces it through passages called water jackets in the engine block. It

collects heat by conduction, and becomes hot itself. Heated coolant then returns to the

radiator for cooling. And the cycle is repeated. Heat is removed from the engine, and

dispersed.

One function of the thermostat is to shorten the warming-up period. It operates

according to coolant temperature. When coolant is cold, it is closed. When a cold engine

starts, coolant circulates within the engine block and cylinder head and through a coolant

bypass to the water pump inlet. It can’t get to the radiator. As the engine warms up, the

coolant trapped in the engine gets hotter and hotter. This starts to open the thermostat,

allowing hot coolant to flow to the radiator.

Components of liquid cooling systems

1. Radiator

It mainly consists of an upper tank and lower tank and between them is a core.

The upper tank is connected to the water outlets from the engines jackets by a hose

pipe and the lover tank is connect to the jacket inlet through water pump by means

of hose pipes. There are 2-types of cores:

i. Tubular

ii. Cellular as shown.

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When the water is flowing down through the radiator core, it is cooled partially

by the fan which blows air and partially by the air flow developed by the forward

motion of the vehicle. As shown through water passages and air passages, wafer

and air will be flowing for cooling purpose. It is to be noted that radiators are

generally made out of copper and brass and their joints are made by soldering.

2. Thermostat Valve

It is a valve which prevents flow of water from the engine to radiator, so that

engine readily reaches to its maximum efficient operating temperature. After attaining

maximum efficient operating temperature, it automatically begins functioning. Generally,

it prevents the water below 70°C.

When the temperature of water increases, the liquid alcohol evaporates and the

bellow expands and in turn opens the butterfly valve, and allows hot water to the

radiator, where it is cooled.

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3. Water Pump

It is used to pump the circulating water. Impeller type pump will be mounted at

the front end. Pump consists of an impeller mounted on a shaft and enclosed in the

pump casing. The pump casing has inlet and outlet openings. The pump is driven by

means of engine output shaft only through belts. When it is driven water will be pumped.

4. Water Jackets

Cooling water jackets are provided around the cylinder, cylinder head, valve

seats and any hot parts which are to be cooled. Heat generated in the engine cylinder,

conducted through the cylinder walls to the jackets. The water flowing through the

jackets absorbs this heat and gets hot. This hot water will then be cooled in the radiator.

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5. Fan

It is driven by the engine output shaft through same belt that drives the pump. It

is provided behind the radiator and it blows air over the radiator for cooling purpose.

Advantages and disadvantages

3. Advantages

i. Uniform cooling of cylinder, cylinder head and valves.

ii. Specific fuel consumption of engine improves by using water cooling system.

iii. If we employ water cooling system, then engine need not be provided at the

front end of moving vehicle.

iv. Engine is less noisy as compared with air cooled engines, as it has water for

damping noise.

4. Disadvantages

i. It depends upon the supply of water.

ii. The water pump which circulates water absorbs considerable power.

iii. If the water cooling system fails then it will result in severe damage of engine.

iv. The water cooling system is costlier as it has more number of parts. Also it

requires more maintenance and care for its parts.

AIRCRAFT EXHAUST SYSTEMS

Engine exhaust systems vent the burned combustion gases overboard, provide heat

for the cabin, and defrost the windscreen. An exhaust system has exhaust piping attached

to the cylinders, as well as a muffler and a muffler shroud. The exhaust gases are pushed

out of the cylinder through the exhaust valve and then through the exhaust pipe system to

the atmosphere.

For cabin heat, outside air is drawn into the air inlet and is ducted through a shroud

around the muffler. The muffler is heated by the exiting exhaust gases and, in turn, heats

the air around the muffler. This heated air is then ducted to the cabin for heat and defrosts

applications. The heat and defrost are controlled in the cockpit, and can be adjusted to the

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desired level.

Exhaust gases contain large amounts of carbon monoxide, which is odorless and

colorless. Carbon monoxide is deadly, and its presence is virtually impossible to detect. The

exhaust system must be in good condition and free of cracks.

Some exhaust systems have an exhaust gas temperature probe. This probe

transmits the exhaust gas temperature (EGT) to an instrument in the cockpit.

The EGT gauge measures the temperature of the gases at the exhaust manifold.

This temperature varies with the ratio of fuel to air entering the cylinders and can be used

as a basis for regulating the fuel/air mixture. The EGT gauge is highly accurate in indicating

the correct mixture setting. When using the EGT to aid in leaning the fuel/air mixture, fuel

consumption can be reduced.

For specific procedures, refer to the manufacturer's recommendations for leaning the

mixture.

STRAIGHT TYPE EXHAUST SYSTEM

Straight exhaust system is means that straight pipe direct connected to the engine

and that is why it is called as straight exhaust system. It is also can be defined as the

exhaust runs straight from the engine to out from under the car without any muffler or

catalytic converter.

STACK TYPE EXHAUST SYSTEM

Stack type exhaust system is defined as a pipe projecting from an aircraft engine

and serving as an outlet for exhaust gases. In other words, short pipes that carry the

exhaust gases from the cylinder into the surrounding air and it is also be called exhaust

pipe. While short stack means the exhaust system of an aircraft reciprocating engine made

of short pipes that direct the exhaust gases from each individual cylinder of the engine away

from the aircraft. Vintage aircraft sometimes have these short stacks on each side of the

engine as 'exhaust'. They do are easy to maintain and inspect, have no back pressure and

keep the exhaust valves cool. But a major drawback is that they are not really quiet. This is

nowadays not the way to go for everyday use aircraft. Besides, it is generally used on non-

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supercharged engines and low powered engines where noise level is not too objectionable.

Moreover, the short stack system is relatively simple, and its removing and installation the

hold-down nuts and clamps.

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COLLECTOR EXHAUST SYSTEM

In automotive engineering, an exhaust manifold collects the exhaust gases from

multiple cylinders into one pipe. Exhaust manifolds are generally simple cast iron or

stainless steel units which collect engine exhaust from multiple cylinders and deliver it to the

exhaust pipe. These consist of individual exhaust head-pipes for each cylinder, which then

usually converge into one tube called a collector. The most common types of aftermarket

headers are made of mild steel or stainless steel tubing for the primary tubes along with flat

flanges and possibly a larger diameter collector made of a similar material as the primaries.

They may be coated with a ceramic-type finish (sometimes both inside and outside), or

painted with a heat-resistant finish, or bare. Chrome plated headers are available but they

will tend to blue after use. Polished stainless steel will also color (usually a yellow tint), but

less than chrome in most cases. Another form of modification used is to insulate a standard

or aftermarket manifold. This decreases the amount of heat given off into the engine bay,

therefore reducing the intake manifold temperature. There are a few types of thermal

insulation but three are particularly common:

i. Ceramic paint is sprayed or brushed onto the manifold and then cured in an

oven. These are usually thin, so have little insulator properties however

reduce engine bay heating by lessening the heat output via radiation.

ii. A ceramic mixture is bonded to the manifold via thermal spraying to give a

tough ceramic coating with very good thermal insulation. This is often used on

performance production cars and track-only racers.

iii. Exhaust wrap is wrapped completely around the manifold. Although this is

cheap and fairly simple, it can lead to premature degradation of the manifold.

The goal of performance exhaust headers is mainly to decrease flow resistance (back

pressure), and to increase the volumetric efficiency of an engine, resulting in a gain in

power output. The processes occurring can be explained by the gas laws, specifically the

ideal gas law and the combined gas law.

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Diamond DA-40 exhausts collector system

Cessna exhausts collector system

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EXHAUST SYSTEM WITH SUPERCHARGER

Firstly, supercharger is an air compressor used for forced induction (the process of

delivering compressed air to the intake of an internal combustion engine) of an internal

combustion engine. A forced induction engine uses a gas compressor to increase the

pressure, temperature and density of the air. Superchargers have almost no lag time to

build pressure because the compressor is always spinning proportionally to the engine

speed.

If you can shove more fuel-air mixture into the cylinder of a piston engine, you will

produce more power and thrust. You need compressed air to keep maximum engine

performance at higher altitudes because the density of air decreases with altitude. Air

density decreases because, as you fly away from the earth, there is less air to pile on top of

the air below it. A supercharger compresses the air back to sea-level-equivalent pressures,

or even much higher, in order to make the engine produce just as much power at cruise

altitude as it does at sea level. With the reduced aerodynamic drag at high altitude and the

engine still producing rated power, a supercharged airplane can fly much faster at altitude

than a naturally aspirated one.

The Impeller in a supercharger's compressor is like the impeller in a hair dryer. Stationary

vanes are added outside the impeller to make the compressor work better.

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Since the size of the supercharger is chosen to produce a given amount of pressure

at high altitude, the supercharger is over-sized for low altitude. The pilot must be careful

with the throttle and watch the manifold pressure gauge to avoid over boosting at low

altitude. As the aircraft climbs and the air density drops, the pilot must continuously open

the throttle in small increments to maintain full power. The altitude at which the throttle

reaches full open and the engine is still producing full rated power is known as the critical

altitude. Above the critical altitude, engine power output will start to drop as the aircraft

continues to climb.

There are at least two different ways to drive the compressor. First is by gear it

directly to the engine’s crankshaft, and second is by letting the gasses that come out the

exhaust pipe spin a fan or turbine that in turn, spins the compressor. For this report, we will

explain on exhaust system with supercharger only. It is called turbo-supercharging. Exhaust

gases coming out of the engines cylinders are sent through a turbine. The turbine’s shaft

then will turns the compressor.

Turbo-supercharging system layout

Turbo-supercharging produces good boost at altitude, the turbine spins faster at

higher altitudes because there is less air pressure restricting the flow out of the exhaust

pipe. Even if there was no natural tendency for the turbine to spin faster, its speed can be

regulated by changing the amount of exhaust that is routed to the turbine.

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Besides altitude performance, a big advantage of turbo-supercharging is that it can

be added externally to existing engine designs. Many modern automotive applications use

turbo-supercharging for boost, just because of this add-on convenience, even though a

geared supercharger would be better in automotive applications. One problem with

Superchargers is that because they spin at such a high rate of speed, they also produce a

lot of heat. Some company’s overcame this obstacle by tapping into the vehicles oil pan to

lubricate the gears inside the head unit of the Supercharger to minimize heat and friction.

Others use internal belts or self-contained head units where the oil never needs to be

changed.

The air itself also becomes hot because you are condensing it. Intercoolers are often

used to cool the air and create a more densely packed air charge. An intercooler is much

like a cars radiator. Two common types of intercoolers are Air-To-Air, which uses outside air

to cool the air that just passed through the Supercharger, and Air-To-Water, which forces

the air through a heat exchanger that is cooled by water. Intercooler are not always needed,

but are usually found on applications that produce higher levels of boost.

You can see the turbo supercharger at the left of the picture is added onto an existing engine. On

the other side of the compressor is the turbine, which is spun by hot exhaust gases.

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Another term you will commonly hear among Supercharger conversations is the

Bypass Valve. When a Supercharger is trying to force air into the engine, but the throttle

shaft is closed, a situation called Compressor Surge is created. This can occur during

deceleration or when the driver is between gears. When the Supercharger is trying to force

the air into a closed throttle body, and the pressure inside the throttle body is greater than

the pressure created by the Supercharger, the air tries to force itself backwards into the

compressor. When this happens, the pressure inside the throttle body is released and the

compressor forces the air back through the Supercharger and then back into the throttle

body again, creating a loop. This is where a Bypass valve comes into play. It’s actuated by

the vacuum from the intake, and then releases the excess pressure either into the

atmosphere (blow off valve) or back through the compressor.

Position of the turbocharger (supercharger driven by exhaust gas)

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REFERENCES

1. Powerplant.pdf

2. www.enginehistory.org/Convention/2005/.../Cooling.pdf

3. http://en.wikipedia.org/wiki/Engine_cooling

4. Reciprocating Machinery Dynamics, Abdulla S. Rangwala, New Age

International, 2006.

5. Pilot’s Handbook of Aeronautical Knowledge, Federal Aviation Administration

(FAA) 2009.

6. www.littleflyers.com/enycool.htm

7. Aviation Maintenance Technician’s Handbook,(FAA) 2008