Fuel Injection Systems of CI Engines

Fuel injection systems of CI EnginesFuel injection systems of CI Engines

CI Engines:CI Engines:

- Compression Ignition Engines- Compression Ignition Engines

- Operated by Diesel cycle.- Operated by Diesel cycle.

- Diesel oil used as fuel- Diesel oil used as fuel

- Combustion of fuel at Constant pressure process.- Combustion of fuel at Constant pressure process.

- Higher order of compression ratio.- Higher order of compression ratio.

- Introduction of fuel at combustion chamber.- Introduction of fuel at combustion chamber.

- Qualitative governing system.- Qualitative governing system.

Introduction:Introduction:

- most vital component - most vital component

- depend on engine performance ie power output, - depend on engine performance ie power output, economy etc.,economy etc.,

- - initiating and controlling of combustion process.initiating and controlling of combustion process.


Injection process:- Amount fuel delivered into air stream is controlled by a pump which forces the fuel under pressure.- fuel injection in fine droplets form- vapourize due to heat transfer from compressed air - form air-fuel mixture.

Functional requirements of an injection system:- accurate metering of fuel injection per cycle.- timing of fuel injection- proper control rate of injection- proper atomization of fuel.- proper spray pattern – ensure rapid mixing of fuel and air.- uniform distribution of fuel droplets.- supply equal quantity of metered fuel to all cylinders- No lag during beginning and end of injection.


Classification of fuel injection systems:- Air injection - Solid injection

Air injection systems:- fuel is forced by means of compressed air.- used nowadays very little, it requires bulky multi stage air compressor.- increase in engine weight and reduces the brake power output.

Advantage:- Good mixing of fuel and air

- higher m.e.p- ability to utilize of fuels of high viscosity – less expensive.-


Solid injection systems:- liquid fuel is injected directly into the combustion chamber w/o aid of compressed air.- hence it is called airless injection systems.

Classification:

- Individual pump- unit Injector- common rail- distributor

Fuel feed systems in CI engines

FUEL FEED SYSTEMS IN CI ENGINESFUEL FEED SYSTEMS IN CI ENGINES

Major equipments used in FI systems:Major equipments used in FI systems:1.1. Fuel Tank:Fuel Tank: For storing the fuel.For storing the fuel.

2.2. Fuel feed pump:Fuel feed pump: To supply the fuel from To supply the fuel from main fuel tank to injection systems.main fuel tank to injection systems.

3.3. Injection pump:Injection pump: To meter and pressurize To meter and pressurize the the fuel for injection.fuel for injection.

4.4. Governor:Governor: To ensure the amount of fuel To ensure the amount of fuel injected in injected in accordance with variation of load.accordance with variation of load.

5.5. Injector:Injector: To take the fuel from the pump and To take the fuel from the pump and distribute it in the CC by atomizing it distribute it in the CC by atomizing it

into fine into fine droplets.droplets.

6.6. Fuel Filters:Fuel Filters: To prevent the dust and To prevent the dust and abrasive abrasive particles to enter the pump - which particles to enter the pump - which minimize the minimize the wear and tear of the components.wear and tear of the components.


Individual pump and Nozzle system:

- each cylinder is provided with one pump and one injector.

- pump is placed close to cylinder.

- HP pump plunger actuated by a cam, and produces the fuel pressure necessary to open the injector valve at the correct time.

- Amount of fuel injected depends on the effective stroke of the plunger.

injectors

HP lines

LP PumpHP Pumps

Fuel in


Unit injector system:- is one in which the pump and injector are in one housing.- each cylinder is provided with one these of injector.- fuel is brought up to the injector by a low pressure pump, a rocker arm actuates the plunger and thus injects the fuel into the cylinder.- amount of fuel is regulated by effective stroke of the plunger.

Injectors with HP Pump

LP lines

LP Pump

Fuel in


Common Line system:- a HP pump supplies fuel under high pressure to a fuel header.- High pressure in the header forces the fuel to each of the nozzles located in the cylinders.- At the proper time, the mechanically operated valve allows the fuel enter the proper cylinder through the nozzle.- The pressure in the fuel header is enough that it must enable to penetrate and disperse the fuel in the combustion chamber.- fuel quantity is regulated by varying the length of the push rod stroke.

injectors

HP lines

HP Pump

Header Fuel In


Fuel Feed Pump:- it is spring loaded type.

- is actuated through a push rod from the crank shaft.

- at the minimum lift position of the cam the spring forces on the plunger creates a suction which causes fuel flow from the main tank into the pump.

- the cam is turned to its maximum lift position, the plunger is lifted upwards.

- At the same time, the inlet valve is closed and the fuel is forced through the outlet valve.

- When the operating pressure gets released, the plunger return spring ceases to function resulting in varying of the pumping stroke under varying engine loads according to the quantity of fuel required by the injection pump.


Objective of fuel injection pump:Objective of fuel injection pump:

- - is to deliver the accurately is to deliver the accurately metered quantity of fuel under metered quantity of fuel under high pressure (120 to 200 bar) at high pressure (120 to 200 bar) at the correct instant to the the correct instant to the injector fitted on each engine injector fitted on each engine cylinder.cylinder.


Fuel injector:

-- Quick and complete combustion is ensured Quick and complete combustion is ensured by the well designed fuel injectorby the well designed fuel injector..

- By atomizing the fuel into fine droplets, it - By atomizing the fuel into fine droplets, it increases the surface area of the fuel increases the surface area of the fuel droplets resulting in better mixing and droplets resulting in better mixing and subsequent combustion.subsequent combustion.

- Atomization is done by forcing the fuel - Atomization is done by forcing the fuel through a small orifice under high pressure.through a small orifice under high pressure.


Nozzle: is the part of an injector through which the liquid fuel is sprayed into the combustion chamber.- Should fulfill the following functions:

1. Atomization of fuel 2. Distribution of fuel3. Injection pressure4. Density of air in the cylinder5. Physical properties of the fuel6. Prevention of impingement on walls7. Mixing

Types of nozzles:1. Pintle Nozzle2. Single hole Nozzle3. Multi-hole Nozzle4. Pintaux Nozzle


TYPES OF NOZZLES


Pintle Nozzle:Pintle Nozzle:The stem of the nozzle valve is extended to form a pin or pintle The stem of the nozzle valve is extended to form a pin or pintle which protrudes through the mouth of the nozzle.which protrudes through the mouth of the nozzle.The size and shape of the pintle can be varied according to the The size and shape of the pintle can be varied according to the requirement.requirement.it provides a spray operating at low injection pressure of 8-10 Mpa.it provides a spray operating at low injection pressure of 8-10 Mpa.The spray cone angle is 60The spray cone angle is 6000

Advantage:Advantage:

It avoids Weak injection and dribbling.It avoids Weak injection and dribbling.It prevents the carbon deposition in the nozzle hole.It prevents the carbon deposition in the nozzle hole.

Single hole nozzle:Single hole nozzle: At the centre of the nozzle there is a single hole which is closed by At the centre of the nozzle there is a single hole which is closed by

nozzle valve.nozzle valve.The size of the hole is usually of the order of 0.2 mm.The size of the hole is usually of the order of 0.2 mm.Injection pressure in the order of 8 - 10 Mpa.Injection pressure in the order of 8 - 10 Mpa.Spray Cone angle is 15Spray Cone angle is 1500..

Disadvantage:Disadvantage:They tend to dribbling.They tend to dribbling.Their spray angle is too narrow to facilitate good mixing unless Their spray angle is too narrow to facilitate good mixing unless higher velocities are used.higher velocities are used.


Multi hole nozzle: It consists of a number of holes are bored at the tip of the nozzle.The number of holes of varied from 4 to 18.The size of the hole are varies in the range of 35 to 200 µm.The hole angle may be from 200 upwards.The nozzle operating at higher pressures of the order of 18 Mpa.

Advantages:in the ability to distribute the fuel properly even with lower air motion available in open combustion chambers.

Pintaux Nozzle: It is a type of Pintle nozzle which has an auxiliary hole drilled in the nozzle body.It injects a small amount of fuel through this additional hole (Pilot injection) in the upstream direction slightly before the main injectionThe nozzle valve does not lift fully at low speeds and most of the fuel is injected through the auxiliary hole.

Advantages:Better starting performance.(20 to 250C)

Disadvantage:Injection characteristics are poorer than the multi hole nozzle


Multi cylinder fuel injection pump


Multi cylinder Engine Fuel injection Pump


FUEL INJECTION TEST RIG

Fuel Injection Systems of CI Engines

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