jj618 notes diesel power plant.doc

JJ618 PLANT ENGINEERING TECHNOLOGYDIESEL POWER PLANT

DIESEL POWER PLANT

1.0 ENGINE CONCEPT

1.1 Internal Combustion engine

The oil engines and gas engines are called Internal Combustion Engines (ICE). In IC engines fuels burn inside the engine and the products of combustion form the working fluid that generates mechanical power. Whereas, in Gas Turbines the combustion occurs in another chamber and hot working fluid containing thermal energy is admitted in turbine. ICE in contrast a steam engine burns its fuel outside the engine.

Oil engines (petrol and diesel) and gas engines (CNG and LPG) are of the same family and have a strong resemblance in principle of operation and construction. The engines convert chemical energy in fuel in to mechanical energy.

A typical oil engine has:1. Cylinder in which fuel and air are admitted and combustion occurs.2. Piston, which receives high pressure of expanding hot products of combustion and the

piston, is forced to linear motion.3. Connecting rod, crankshaft linkage to convert reciprocating motion into rotary motion ofshaft.4. Connected Load, mechanical drive or electrical generator.5. Suitable valves (ports) for control of flow of fuel, air, exhaust gases, fuel injection, and

ignition systems.6. Lubricating system, cooling system

In an engine-generator set, the generator shaft is coupled to the engine shaft.

The most common ICE engines is diesel engine, petrol engine and gas turbine. The gas turbine we had discuss in previous chapter.

1.2 Different Between Petrol Engine and Diesel Engine

The main differences between the petrol engine and the diesel engine are:1. A gasoline engine intakes a mixture of gas and air, compresses it and ignites the mixture

with a spark. A diesel engine takes in just air, compresses it and then injects fuel into the compressed air. The heat of the compressed air lights the fuel spontaneously.

2. A gasoline engine compresses at a ratio of 8:1 to 12:1, while a diesel engine compresses at a ratio of 14:1 to as high as 25:1. The higher compression ratio of the diesel engine leads to better efficiency.

3. Gasoline engines generally use either carburetion, in which the air and fuel is mixed long before the air enters the cylinder, or port fuel injection, in which the fuel is injected just prior to the intake stroke (outside the cylinder). Diesel engines use direct fuel injection to the diesel fuel is injected directly into the cylinder.

POLITEKNIK SULTAN MIZAN ZAINAL ABIDIN, DUNGUNPERKASA DENGAN TEKNOLOGI DAN IMAN

http://inventors.about.com/library/inventors/blsteamengine.htm


1.3 Four-Stroke Cycle

Four stroke petrol engine operation

In the INTAKE Stroke air fuel mixture is sucked in through the intake port (valve) which is on top of the cylinder in to to the chamber (cylinder) when the piston is moving down. The exhaust port is closed. The ports (valves) are opened and closed through the lifter resting on camshaft. As the cam turns the lifters get lifted and put back down. The cam is turned by it being connected to the crank by the cam belt. And as the cam shaft gear is bigger it turns at half the speed of the crank.

Once the piston reaches Bottom Dead Center (BDC) the top half of the cylinder is filled with the as much air-fuel mixture it can take which is ready to be compressed. Only the top half gets filled as the piston rings prevent air-fuel mixture going to the bottom through the edges of piston. At this point the inlet valve gets closed up. This is the end of the INTAKE stroke.

Now the piston starts to travel upwards to Top Dead Center (TDC) which starts the COMPRESSION stroke. As the piston rises up it compresses the air fuel, at this point both intake and exhaust ports are closed.

Just before TDC spark plug ignites air-fuel mixture through ignition system sending a high voltage to spark plug. BANG. Because of air-fuel mixture igniting their is a release of heat and because of pressure send's the piston back down. This is the POWER stroke.

Once the piston reaches BDC again the exhaust valve opens up releasing pressure inside the cylinder. Piston starts to move up and pushes burnt gases out through the exhaust port through to the exhaust system. This is the EXHAUST stroke.

Once the piston reaches TD. the exhaust port closes and inlet valve opens up, and we come back to the INTAKE stroke.



1.4 Two-Stroke Cycle

Two stroke petrol fulled engine operation

StrokePiston

Direction

Actions Occurring during

This StrokeExplanation

Stroke 1

Piston travels up the

cylinder barrel

Induction & Compression

As the piston travels up the barrel, fresh fuel/air mix is sucked into the crankcase (bottom of the engine) & the fuel/air mix in the cylinder (top of the engine) is compressed ready for ignition

Stroke 2

Piston travels down the cylinder barrel

Ignition & Exhaust

The spark plug ignites the fuel/air mix in the cylinder, the resulting explosion pushes the piston back down to the bottom of the cylinder, as the piston travels down, the transfer port openings are exposed & the fresh fuel/air mix is sucked from the crankcase into the cylinder. As the fresh fuel/air mix is drawn into the cylinder, it forces the spent exhaust gases out through the exhaust port.

Two stroke petrol fulled engine operation explanation

2.0 DIESEL POWER PLANT

2.1 Advantages and Disadvantages of Diesel Power Plant



The advantages of diesel power plants are listed below.1. Very simple design also simple installation.2. Limited cooling water requirement.3. Standby losses are less as compared to other Power plants.4. Quickly started and put on load.5. Smaller storage is needed for the fuel.6. Layout of power plant is quite simple.7. There is no problem of ash handling.8. Less supervision required.9. For small capacity, diesel power plant is more efficient as compared to steam power plant.10. They can respond to varying loads without any difficulty.

The disadvantages of diesel power plants are listed below.1. High maintenance and operating cost.2. Fuel cost is more, diesel is costly.3. The plant cost per kW is comparatively more.4. The life of diesel power plant is small due to high maintenance.5. Noise is a serious problem in diesel power plant.6. Diesel power plant cannot be constructed for large scale.

3.0 DIESEL CYCLE

3.1 Air Standard Power Cycle

Spark-ignition engines, diesel engines, and conventional gas turbines are familiar examples of devices that operate on gas cycles. In all these engines, energy is provided by burning a fuel within the system boundaries. That is, they are internal combustion engines. Because of this combustion process, the composition of the working fluid changes from air and fuel to combustion products during the course of the cycle. Even though internal combustion engines operate on a mechanical cycle (the piston returns to its starting position at the end of each revolution), the working fluid does not undergo a complete thermodynamic cycle. It is thrown out of the engine at some point in the cycle (as exhaust gases) instead of being returned to the initial state. Working on an open cycle is the characteristic of all internal combustion engines. The actual gas power cycles are rather complex. To reduce the analysis to a manageable level, we utilize the following approximations, commonly known as the air-standard assumptions:

• The working fluid is air, which continuously circulates in a closed loop and always behaves as an ideal gas. • All the processes that make up the cycle are internally reversible. • The exhaust process is replaced by a heat-rejection process that restores the working fluid to its initial state. • The combustion process is replaced by a heat-addition process from an external source.

The concept of standard air power cycle



Another assumption that is often utilized to simplify the analysis even more is that air has constant specific heats whose values are determined at room temperature (25°C, or 77°F). When this assumption is utilized, the air-standard assumptions are called the cold-air-standard assumptions. A cycle for which the air-standard assumptions are applicable is frequently referred to as an air-standard cycle. The air-standard assumptions previously stated provide considerable simplification in the analysis without significantly deviating from the actual cycles. This simplified model enables us to study qualitatively the influence of major parameters on the performance of the actual engines.

3.2 Diesel Power Cycle

The Diesel cycle is the ideal cycle for Compression Ignition (CI) reciprocating engines. The CI engine, first proposed by Rudolph Diesel in the 1890s, is very similar to the Spark Ignition (SI) engine (petrol or gasoline engine), differing mainly in the method of initiating combustion. In spark-ignition engines, the air–fuel mixture is compressed to a temperature that is below the auto-ignition temperature of the fuel, and the combustion process is initiated by firing a spark plug. In CI engines, the air is compressed to a temperature that is above the auto-ignition temperature of the fuel, and combustion starts on contact as the fuel is injected into this hot air. Therefore, the spark plug and carburetor are replaced by a fuel injector in diesel engines.

Gasoline and Diesel engine ignition system

In gasoline engines, a mixture of air and fuel is compressed during the compression stroke, and the compression ratios are limited by the onset of auto-ignition or engine knock. In diesel engines, only air is compressed during the compression stroke, eliminating the possibility of auto-ignition. Therefore, diesel engines can be designed to operate at much higher compression ratios, typically between 12 and 24. Not having to deal with the problem of auto-ignition has another benefit: many of the stringent requirements placed on the gasoline can now be removed, and fuels that are less refined (thus less expensive) can be used in diesel engines.

The fuel injection process in diesel engines starts when the piston approaches TDC and continues during the first part of the power stroke. Therefore, the combustion process in these engines takes place over a longer interval. Because of this longer duration, the combustion process in the ideal Diesel cycle is approximated as a constant-pressure heat-addition process.



In fact, this is the only process where the Otto and the Diesel cycles differ. The remaining three processes are the same for both ideal cycles. That is, process 1-2 is isentropic compression 2-3 is constant volume heat addition 3-4 is isentropic expansion 4-1 is constant-volume heat rejection.

The similarity between the two cycles is also apparent from the P-v and T-s diagrams of the Diesel cycle, shown in figure below.

T-s and P-v diagrams for the ideal Diesel cycle.

3.3 Dual Power Cycle

Approximating the combustion process in internal combustion engines as a constant-volume or a constant-pressure heat-addition process is overly simplistic and not quite realistic. Probably a better (but slightly more complex) approach would be to model the combustion process in both gasoline and diesel engines as a combination of two heat-transfer processes, one at constant volume and the other at constant pressure. The ideal cycle based on this concept is called the dual cycle, and a P-v diagram for it is given in figure below.



p–v and T–s diagrams of the air-standard dual cycle.

As in the Otto and Diesel cycles, Process 1-2 is an isentropic compression. Process 2-3 is a constant-volume heat addition Process 3-4 is a constant pressure heat addition Process 3-4 also makes up the first part of the power stroke. The isentropic expansion from

state 4 to state 5 is the remainder of the power stroke. As in the Otto and Diesel cycles, the cycle is completed by a constant volume heat rejection process,

Process 5-1. Areas on the T–s and p–v diagrams can be interpreted as heat and work, respectively, as in the cases of the Otto and Diesel cycles.

4.0 DIESEL POWER PLANT LAYOUT

4.1 Fuel Supply System

The fuel is delivered to the plant by railroad tank car, by truck or by barge and tanker and storedin the bulk storage situated outdoors for the sake of safety. From this main fuel tank, the fuel oil istransferred to the daily consumption tank by a transfer pump through a filter. The capacity of the daily consumption should be at least the 8-hour requirement of the plant. This tank is located either above the engine level so that the fuel flows by gravity to the injection pump or below the engine level and the fuel oil is delivered to the injection pump by a transfer pump driven from the engine shaft.

Fuel connection is normally used when tank-car siding or truck roadway is above tank level. If it is below tank level, then, an unloading pump is used to transfer fuel form tank car to the storage tank (dotted line).



Fuel supply system layout

4.2 Fuel Injection System

The five essential functions of a fuel injection system are:1. To deliver oil from the storage to the fuel injector.2. To raise the fuel pressure to the level required for atomization.3. To measure and control the amount of fuel admitted in each cycle.4. To control time of injection.5. To spray fuel into the cylinder in atomized form for thorough mixing and burning.

The above functions can be achieved in a variety of ways. The following are the systems, whichare usual on power station diesels:1. Common Rail.2. Individual Pump Injection.3. Distributor.

4.2.1 Common Rail Injection

A typical common rail injection system is shown in figure below. It incorporates a pump with built inpressure regulation, which adjusts pumping rate to maintain the desired injection pressure. The function of the pressure relief and timing valves is to regulate the injection time and amount.

Spring-loaded spray valve acts merely as a check. When injection valve lifts to admit high-pressure fuel to spray valve, its needle rises against the spring. When the pressure is vented to the atmosphere, the spring shuts the valve.



Common rail injection

4.2.2 Individual Pump injection

In this system, each fuel nozzle is connected to a separate injection pump. The pumpitself does the measuring of the fuel charge and control of the injection timing. The delivery valve in the nozzle is actuated by fuel-oil pressure.

Individual pump injection

4.2.3 Distributor System



This system is shown in figure below. In this system, the fuel is metered at a central point i.e., the pump that pressurizes, meters the fuel and times the injection. From here, the fuel is distributed tocylinders in correct firing order by cam operated poppet valves, which open to admit fuel to nozzles.

Distributor System

4.2 Intake and Admission System

Generally a large diesel engine requires 0.076 to 0.114 m3 of air per min per kw of power developed. The fresh air is drawn through pipes or ducts or filters. The purpose of the filter is to catch any air borne dirt as it otherwise may cause the wear and tear of the engine. The filters may be of dry or oil bath. The filters should be cleaned periodically.

Electrostatic precipitator filters can also be used. Oil impingement type of filter consists of a frame filled with metal shavings which are coated with a special oil so that the air in passing through the frame and being broken up into a number of small filaments comes into contact with the oil whose property is to seize and hold any dust particles being carried by the air.

The dry type of filter is made of cloth, felt, glass wool etc. In case of oil bath type of filter the air is swept over or through a pool of oil so that the particles of dust become coated. Lightweight steel pipe is the material for intake ducts.

Since the noise may be transmitted back to the outside air via the air intake. So, a silencer isneeded in between the engine and the intake system.

There should be minimum pressure loss in the air intake system, otherwise specific fuel consumption will increase and the engine capacity is reduced.



Air Intake System for Diesel Power Plant

The air intake system conveys fresh air through pipes or ducts to:1. Air-intake manifold of four-stroke engine.2. The scavenging pump inlet of a two-stroke engine.3. The supercharger inlet of a supercharged engine.

The air intake may be located:1. Very Near the ground and outside the plant building.2. In the building roof.3. On the building roof.

Following precautions should be taken while constructing a suitable air intake system:1. They do not locate the air-intakes inside the engine room.2. Do not take air from a confined space as otherwise serious vibration problems can occur due

to air pulsations.3. Do not use air-intake line with too small a diameter or which is too long, otherwise engine

starvation might occur.4. Do not install air-intake filters in an inaccessible location.5. Do not locate the air intake filters close to the roof of the engine room since serious

vibrations of the roof may occur due to pulsating airflow through the filters.

4.3 Exhaust System

The purpose of the exhaust system is to discharge the engine exhaust to the atmosphere outsidethe main building. For designing of exhaust system of a big power plant, following points should be taken into consideration1. Exhaust noise should be reduced to a tolerable degree.2. To reduce the air pollution at breathing level, Exhaust should be exhausted well above the

ground level3. Pressure loss in the system should be reduced to minimum.4. By use of flexible exhaust pipe, the vibrations of exhaust system must be isolated from the

plant.5. A provision should be made to extract the heat from exhaust if the heating is required for fuel

oil heating or building heating or process heating.

In many cases, we have seen that the temperature of the exhaust gases under full load conditionsmay be of the order of 400°C. With the recovery of heat from hot jacket water and exhaust gases and its use either for heating oil or buildings in cold weather increase the thermal efficiency to 80%.



Nearly 40% of the heat in the fuel can be recovered from the hot jacket water and exhaust gases. The heat from the exhaust can also be used for generating the steam at low pressure that can be used for process heating. Nearly 2 kg of steam at 8 kg/cm2 can be generated per kW per hour, when the mass of exhaust gases can be taken as 10 kg/kW hr.

4.4 Cooling System

During combustion process the peak gas temperature in the cylinder of an internal combustionengine is of the order of 2500 K. Maximum metal temperature for the inside of the combustion chamber space are limited to much lower values than the gas temperature by a large number of considerations and thus cooling for the cylinder head, cylinder and piston must therefore be provided.

Necessity of engine cooling arises due to the following facts:

1. During combustion period, the heat fluxes to the chamber walls can reach as high as 10 mW/m2. The flux varies substantially with location. The regions of the chamber that are contacted by rapidly moving high temperature gases generally experience the highest fluxes. In region of high heat flux, thermal stresses must be kept below levels that would cause fatigue cracking. So temperatures must be less than about 400°C for cast iron and 300°C for aluminium alloy for water cooled engines. For air-cooled engines, these values are 270°C and 200°C respectively.

2. The gas side surface temperature of the cylinder wall is limited by the type of lubricating oil used and this temperature ranges from 160°C to 180°C. Beyond these temperature, the properties of lubricating oil deteriorates very rapidly and it might even evaporates and burn, damaging piston and cylinder surfaces. Piston seizure due to overheating resulting from the failure of lubrication is quite common.

3. The valves may be kept cool to avoid knock and pre-ignition problems which result from overheated exhaust valves (true for S.I. engines).

4. The volumetric and thermal efficiency and power output of the engines decrease with an increase in cylinder and head temperature.

Based on cooling medium two types of cooling systems are in general use. They are1. Air as direct cooling system.2. Liquid or indirect cooling system.

Air-cooling is used in small engines and portable engines by providing fins on the cylinder. Bigdiesel engines are always liquid (water/special liquid) cooled. Liquid cooling system is further classified as1. Open cooling system2. Natural circulation (Thermo-system)3. Forced circulation system

4.4.1 Open Cooling System

This system is applicable only where plenty of water is available. The water from the storagetank is directly supplied through an inlet valve to the engine cooling water jacket. The hot water coming out of the engine is not cooled for reuse but it is discharged.



4.4.2 Natural Circulation Cooling System

The system is closed one and designed so that the water may circulate naturally because of thedifference in density of water at different temperatures. Figure below shows a natural circulation cooling system. It consists of water jacket, radiator and a fan. When the water is heated, its density decreases and it tends to rise, while the colder molecules tend to sink. Circulation of water then is obtained as the water heated in the water jacket tends to rise and the water cooled in the radiator with the help of air passing over the radiator either by ram effect or by fan or jointly tends to sink. Arrows show the direction of natural circulation, which is slow.

Natural circulation cooling system

4.4.3 Forced Circulation Cooling System

Fig. below shows forced circulation cooling system that is closed one. The system consists ofpump, water jacket in the cylinder, radiator, fan and a thermostat. The coolant (water or synthetic coolant) is circulated through the cylinder jacket with the help of a pump, which is usually a centrifugal type, and driven by the engine. The function of thermostat, which is fitted in the upper hose connection initially, prevents the circulation of water below a certain temperature (usually upto 85°C) through the radiation so that water gets heated up quickly.

Standby diesel power plants upto 200 kVA use this type of cooling. In the case of bigger plant,the hot water is cooled in a cooling tower and recirculated again. There is a need of small quantity of cooling make-up water.



Forced Circulation Cooling System.

4.5 Lubricating System

Since frictional forces causes wear and tear of rubbing parts of the engine and thereby the life ofthe engine is reduced. So the rubbing part requires that some substance should be introduced between the rubbing surfaces in order to decrease the frictional force between them. Such substance is called lubricant. The lubricant forms a thin film between the rubbing surfaces. And lubricant prevents metalto-metal contact. So we can say “Lubrication is the admission of oil between two surface having relative motion”.

The main function of lubricant is to,1. To reduce friction and wear between the parts having relative motion by minimizing the force

of friction and ensures smooth running of parts.2. To seal a space adjoining the surfaces such as piston rings and cylinder liner.3. To clean the surface by carrying away the carbon and metal particles caused by wear.4. To absorb shock between bearings and other parts and consequently reduce noise.5. To cool the surfaces by carrying away heat generated due to friction.6. It helps the piston ring to seal the gases in the cylinder.7. It removes the heat generated due to friction and keeps the parts cool.

The various parts of an engine requiring lubrication are;1. Cylinder walls and pistons.2. Main crankshaft bearings.3. Piston rings and cylinder walls.4. Big end bearing and crank pins.5. Small end bearing and gudge on pin bearings.



6. Main bearing cams and bearing valve tappet and guides7. Timing gears etc.8. Camshaft and cam shaft bearings.9. Valve mechanism and rocker arms.

A good lubricant should possess the following properties:1. It should not change its state with change in temperature.2. It should maintain a continuous film between the rubbing surfaces.3. t should have high specific heat so that it can remove maximum amount of heat.4. It should be free from corrosive acids.5. The lubricant should be purified before it enters the engine.6. It should be free from dust, moisture, metallic chips, etc.

The cooling water used in the engine may be used for cooling the lubricant. Nearly 2.5% of heatof fuel is dissipated as heat, which is removed by the lubricating oil.

The various lubricants used in engines are of three types:1. Liquid lubricants or wet sump lubrication system.2. Solid lubricants or dry sump lubrication system.3. Semi-solid lubricants or mist lubrication system.

Liquid oils lubricants are most commonly used. Liquid lubricants are of two types:1. Mineral oils2. Fatty oils.

Graphite, white lead and mica are the solid lubricants.

Semi solid lubricants or greases as they are often called are made from mineral oils and fatty-oils.

4.5.1 Liquid Lubrication or wet Sump Lubrication System

These systems employ a large capacity oil sump at the base of crank chamber, from which the oilis drawn by a low-pressure oil pump and delivered to various parts. Oil then gradually returns back to the sump after serving the purpose.

(a) Splash system. This system is used on some small four strokes, stationary engines. In this case the caps on the big ends bearings of connecting rods are provided with scoops which, when the connecting rod is in the lowest position, just dip into oil troughs and thus directs the oil through holes in the caps to the big end bearings. Due to splash of oil it reaches the lower portion of the cylinder walls, crankshaft and other parts requiring lubrication. Surplus oil eventually flows back to the oil sump.

Oil level in the troughs is maintained by means of an oil pump which takes oil from sump, through a filter. Splash system is suitable for low and medium speed engines having moderate bearing load pressures. For high performance engines, which normally operate at high bearing pressures and rubbing speeds this system does not serve the purpose.

(b) Semi-pressure system. This method is a combination of splash and pressure systems. It incorporates the advantages of both. In this case main supply of oil is located in the base of crank chamber. Oil is drawn from the lower portion of the sump through a filter and is delivered by means of a gear pump at pressure of about 1 bar to the main bearings. The big end bearings are lubricated by means of a spray through nozzles. Thus oil also lubricates the cams, crankshaft bearings, cylinder walls and timing gears. An oil pressure gauge is provided to indicate satisfactory oil supply.



The system is less costly to install as compared to pressure system. It enables higher bearingloads and engine speeds to be employed as compared to splash system.

Semi Pressure System.

(c) Full pressure system. In this system, oil from oil sump is pumped under pressure to the various parts requiring lubrication. Refer figure below. The oil is drawn from the sump through filter and pumped by means of a gear pump. The pressure pump at pressure ranging delivers oil from 1.5 to 4 bar. The oil under pressure is supplied to main bearings of crankshaft and camshaft. Holes drilled through the main crankshafts bearing journals, communicate oil to the big end bearings and also small endbearings through holes drilled in connecting rods. A pressure gauge is provided to confirm the circulation of oil to the various parts. A pressure-regulating valve is also provided on the delivery side of this pump to prevent excessive pressure.



Full Pressure System.

This system finds favor from most of the engine manufacturers as it allows high bearing pressureand rubbing speeds.

The general arrangement of wet sump lubrication system is shown in figure below. In this case oil isalways contained in the sump that is drawn by the pump through a strainer.

Wet sump lubrication system.



4.5.2 Solid Lubricants or Dry Sump Lubrication System

Refer figure below. In this system, the oil from the sump is carried to a separate storage tank outside the engine cylinder block. The oil from sump is pumped by means of a sump pump through filters to the storage tank. Oil from storage tank is pumped to the engine cylinder through oil cooler. Oil pressure may vary from 3 to 8 kgf/cm2. Dry sump lubrication system is generally adopted for high capacity engines.

Dry Sump Lubrications System.

4.5.2 Mist Lubrication System

This system is used for two stroke cycle engines. Most of these engines are crank charged, i.e.,they employ crank case compression and thus, are not suitable for crank case lubrication. These engines are lubricated by adding 2 to 3 per cent lubricating oil in the fuel tank. The oil and fuel mixture is induced through the carburator. The gasoline is vaporized; and the oil in the form of mist, goes via crankcase into the cylinder. The oil that impinges on the crank case walls lubricates the main and connecting rod bearings, and rest of the oil that passes on the cylinder during charging and scavenging periods, lubricates the piston, piston rings and the cylinder.

4.6 Engine Starting System

This is an arrangement to rotate the engine initially, while starting, until firing starts and the unit runs with its own power. Small sets are started manually by handles but for larger units, compressed air is used for starting. In the latter case, air at high pressure is admitted to a few of the cylinders, making them to act as reciprocating air motors to turn over the engine shaft. The fuel is admitted to the remaining cylinders which makes the engine to start under its own power.

Starting Circuits Diesel engines have as many different types of starting circuits as there aretypes, sizes, and manufacturers of diesel engines. Commonly, they can be started by air motors, electric motors, hydraulic motors, and manually. The start circuit can be a simple manual start



pushbutton, or a complex auto-start circuit. But in almost all cases the following events must occur for the starting engine to start.

1. The start signal is sent to the starting motor. The air, electric,or hydraulic motor, will engage the engine flywheel

2. The starting motor will crank the engine. The starting motor will spin the engine at a high enough rpm to allow the engines compression to ignite the fuel and start the engine running.

3. The engine will then accelerate to idle speed. When the starter motor is overdriven by the running motor it will disengage the flywheel. Because a diesel engine relies on compression heat to ignite the fuel, a cold engine can rob enough heat from the gasses that the compressed air falls below the ignition temperature of the fuel. To help overcome this condition, some engines (usually small to medium sized engines) have glow plugs. Glow plugs are located in the cylinder head of the combustion chamber and use electricity to heat up the electrode at the top of the glow plug.

The heat added by the glow plug is sufficient to help ignite the fuel in the cold engine. Once the engine is running, the glow plugs are turned off and the heat of combustion is sufficient to heat the block and keep the engine running. Large engines usually heat the block and/or

have powerful starting motors that are able to spin the engine long enough to allow the compression heat to fire the engine. Some large engines use air start manifolds that inject compressed air into the cylinders which rotates the engine during the start sequence

Glow plug


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