Date post: | 19-Dec-2015 |
Category: |
Documents |
Upload: | jordan-price |
View: | 218 times |
Download: | 1 times |
Diesel Fuel
If you have ever compared diesel fuel and gasoline, you know that they are different .They certainly smell different .Diesel fuel is heavier and oilier .
Diesel fuel evaporates much more slowly than gasoline -- its boiling point is actually
higher than the boiling point of water .You will often hear diesel fuel referred to as
"diesel oil" because it is so oily .
Diesel fuel evaporates more slowly because it is heavier .
It contains more carbon atoms in longer chains than gasoline does (gasoline is typically C9H20, while diesel fuel is typically C14H30) .
It takes less refining to create diesel fuel, which is why it is generally cheaper than gasoline .
DIESEL FUEL
Diesel fuel must meet an entirely different set of standards than gasoline .The fuel in a diesel engine is not ignited with a spark, but is ignited by the heat
generated by high compression .All diesel fuel must be clean, be able to flow at low temperatures, and be of the proper cetane rating.Cleanliness .Low-temperature fluidity .
Cetane number.
Diesel Fuel CharacteristicsCetane numberMeasure of relative ease to initiate combustionHigher number: easier to ignite
Octane number for gas: oppositeHigher number: less tendency to ignite
Cetane NumberIgnition quality measureAffects: cold starting, warm-up, combustion roughness, acceleration, and exhaust smoke densityCetane number is based on the ignition characteristics of two hydrocarbons:
Cetane - short delay period and ignites readily (100)Alphamethylnaphthalene (AMN) - long delay period and poor ignition quality (0)It is the percentage by volume of normal cetane in a blend with AMN
PC engines require a minimum cetane no. of 35DI engines require a minimum cetane no. of 40
Cetane NumberHigh cetane number indicates good ignition quality (short delay period)Low cetane number indicates poor ignition quality (long delay period)
PC engines require a minimum cetane # of 35
DI engines require a minimum cetane # of 40Cetane improver additive can improve ignition quality and reduce white smoke during start up
Fuel Injection In CI Engines
Delay Period
Rapid Combustion - knock
Diffusion Combustion - smoke
Cylinder Pressure
Fuel Injection In CI Engines
Less air means less fuel required
Fuel injection system has to compensate for air
density to minimize smoke output
7% decrease in air density per 1000m altitude
FUEL FILTERS
The fuel filtration and water separation needs of today's new generation
diesel fuel systems demand extremely high efficiency, flexibility, multiple
functions and ease of use with no risk of fuel spills or contaminated parts.
Stan dyne's patented Fuel Manager® range of Available for light, medium and heavy duty trucks; and agricultural,industrial, construction and marine
applications, there is a Fuel Manager
The FM10 Series is designed for diesel engines with a fuel flow rate up
to 50 US gallons/hr (190 liters/hr). Typical engines range from 10 to 200 HP The FM100 Series is designed for
diesel engines with a fuel flow rate upto 80 US gallons/hr (300 liters/hr). Typical engines range from 50 to 350 HP.
The FM1000 Series is designed for diesel engines with a fuel flow rateup to 180 US gallons/hr (680 liters/hr). Typical engines range from 200 to
Fuel pump
The ‘traditional’ style of injection pump is the in-line pump. They have been used for many
decades and are still commonly found on agricultural and stationary diesels, and very many older
model diesel road vehicles still employ them, including the Toyota Landcruiser 2H diesel.. They
are typically capable of generating injection nozzle pressures up to about 750 bar in light road
vehicles – towards the lower end of the range that is required these days.
They have a separate pump plunger for each cylinder of the engine, so a 4 cylinder engine has a four plunger pump, a 6 cylinder engine has a six plunger pump, etc. The pump is run at half engine crankshaft speed and has a central shaft with four/six etc. cam lobes attached. So, each plunger is operated by it’s cam once every two crankshaft revolutions, coinciding of course with the power stroke of its engine cylinder. Each plunger has a spiral groove or helix machined on it’s side and cut through to the top of the plunger. When operated, the plunger is pushed up by its cam lobe. At a certain point the spiral groove will line up with a spill port on the side of the plunger cylinder and the rest of the fuel is ‘spilled’.
Because the groove is a spiral shape, the point in the plunger stroke when it uncovers the spill port
will vary as the plunger is rotated a few degrees either way. This adjusts the spill point and hence,
the volume of its fuel charge to the engine cylinder.
So that all engine cylinders receive the same sized fuel charge, all of the plungers are rotated
together. This is achieved by each plunger having gear teeth machined to it’s circumference which
are engaged by a common gear rack which runs through the pump body. As the rack moves back
and forth, all four (or six or more) plungers are rotated together. The extremes of travel of the
pump rack control the minimum and maximum fuel charge quantities the pump is capable of
PRE SUPPLY PUMP
The electric fuel pump comprises of:1.Electric Motor
2.Roller-Cell Pump3.Non Return Valve
The roller cell is driven by an electric motor.
Its rotor is mounted eccentrically and provided with slots in which movable rollers are free to travel.
PRE SUPPLY PUMP
The rollers are forced against the base plate by rotation and by fuel pressure.
The fuel is transported to the outlet openings on the pump’s pressure side.
PRE SUPPLY PUMP
Gear type fuel pump The drive gear
wheel is driven by the engine.
Delivery quantity is directly proportional
to engine speed. Shut off is by means
of an electromagnet..
PRE SUPPLY PUMPvariants
High- pressure pump
The pump plunger moves downwards The inlet valve opens
The fuel is drawn in to the pumping element chamber(suction stroke)
At BDC, the inlet valve closes The fuel in the chamber can be compressed
by the upward moving plunger.
High- pressure pump
Rail is a forged-steel tube.ID is approx.. 10mmLength is between 280 and 600mm
The volume must be “ as small as possible, as large as necessary”
High- pressure accumulator (Rail)
Pressure-control valve (DRV)
Responsible for maintaining the pressure in the rail at a constant level.
The injector on a diesel engine is its most complex component and has been the subject of a great deal of experimentation -- in any particular engine it may be located in a variety of places .
The injector has to be able to withstand the temperature and pressure inside the cylinder and still deliver the fuel in a fine mist .
Fuel Injector
Getting the mist circulated in the cylinder so that it is evenly distributed is also a problem, so some diesel engines employ special induction valves, pre-combustion chambers or other devices to swirl the air in the combustion chamber or otherwise improve the ignition and combustion process .
CI Engine Combustion Chambers
Two types:Indirect (divided
chamber) injection - into a pre-
combustion chamber
Combustion Chamber Comparison
IndirectGood
Excellent mixing, turbulence characteristics
Can burn lower quality fuelLower injection pressureLess pronounced knock
Combustion Chamber Comparison
IndirectBad
Very high temperature/pressure in injection chamber
Higher emissions, especially NOx
Harder to start - glow plugsLess efficient
Combustion Chamber Comparison
DirectBad
Pressure rise can be great, knock
High injection pressure, high quality fuel
Combustion Chamber Comparison
DirectGood
Lower specific fuel consumption - 20%
Lower emissionsBigger valves, higher
volumetric efficiency
Direct Injection
Air-fuel mixing importantControlled by:
Use of swirl-inducing designsIntake port geometryPiston cap geometry
Injection system designHigh pressureMany nozzle holesPositioning
Bad: high-tech injection system
Good: Higher volumetric efficiency
DIESEL ENGINESIndirect and Direct Injection
FIGURE 4-4 A direct injection diesel engine injects the fuel directly into the combustion
chamber. Many designs do not use a glow plug.
DIESEL ENGINESIndirect and Direct Injection
In an indirect injection
(abbreviated IDI) diesel engine, fuel is injected into a small
prechamber, which is connected to the
cylinder by a narrow opening .
The initial combustion takes place in this
prechamber .This has the effect of
slowing the rate of combustion, which
tends to reduce noise. FIGURE 4-3 An indirect injection diesel engine uses a prechamber and a glow
plug.
DIESEL ENGINESDiesel Fuel Ignition
Ignition occurs in a diesel engine by injecting fuel into the air charge,
which has been heated by compression to a temperature
greater than the ignition point of the fuel or about 1,000°F (538°C).
Roger Krieger, GM R&D Center
Fuel Injection Systems
Electronic distributor pump
Electronic unit injector (EUI)
High-pressure common rail