Diesel Fuel System

Diesel Fuel System

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During this lesson you will be able to..

• Understand how a diesel engine completes the combustion process

• Explain the difference between gasoline and diesel fuels

• Compare the differences between the gasoline fuel system and diesel fuel system

Crude Oil

• Keep in mind gasoline and diesel both originate from crude oil

Diesel Fuel Vs Gasoline

• Less Popular that gasoline

• 1 Gallon of diesel fuel contains more heat energy that 1 gallon of gasoline

• Diesel fuel can produce more cylinder pressure and vehicle movement than gasoline

• Thicker consistency that gasoline

Open Ended

Before we get deep into this subject. Why do you think diesel is not as popular as gasoline?

Open Ended

Since diesel fuel is thicker and has a different burning characteristic, do you think any modifications would have to be made to the fuel system components. If so, what part(s) what need to be changed?

Diesel Fuel System Basics

• Since the diesel fuel is thicker and has a different burring characteristic, a high pressure injection system must be used.

• This system injects high-pressure fuel directly into the combustion chambers

Diesel Fuel Strategy

• Diesel fuel will not vaporize as easily as gasoline
• If the diesel fuel were to enter the engine at low pressure it collect on the cylinder walls and not combust correctly

One of the keys to a correctly operating diesel engine is proper fuel atomization or vaporization

Open Ended

Do you think vaporizing the fuel at high pressure would result in a positive or negative effect on the fuel ability to mix with the air and why?

Diesel Fuel Grade

Diesel fuel has uniform standards to ensure it meets the needs of the engines There are 3 Diesel Fuel Grades No. 1 No. 2 No. 4

If there is only one option at the pump then why are there different grades?

• No 2 Diesel is what is sold at the pumps

• Has a medium viscosity and widest range of operating conditions

Cloud Point

• Diesel fuel contains paraffin (wax)
• At low temperatures the wax separates from the fuel turning the fuel cloudy or milky
• The temperature at which this happens is caused cloud point
• Often referred to as "gelling"
• Kind of like bacon grease

Water Contamination

• When water and diesel mix it causes filter clogs and corroded components

• Many parts of the fuel system are very precise and any little imperfection causes major problems

• Newer diesels feature water separators t remove water from the fuel

• Diesel fuel attracts moisture if left in a open container

Open Ended

List one advantage to diesel fuel and one disadvantage of diesel fuel compared to gasoline.

Cetane Ratings

• Cold starting ability of the diesel fuel

• The higher the number the easier the engine will start and run in cold weather

• Normal rating around 45 Cetane (common with No2 Diesel)

• 
  

That is it for diesel fuel, lets see how a diesel actually works

Let's Start with reviewing the gasoline combustion process

• Intake (Air/Fuel Enters)

• Compression (Air is squeezed)

• Power (Combustion)

• Exhaust (Burnt Air/Fuel Exit)

Multiple Choice

What is the main event that starts the power/combustion stroke?

• Spark

• Fuel entering the cylinder

• Air entering the cylinder

• Burnt air/fuel exiting the exhuast

Look for the differences

Open Ended

List any similarities or differences in the components or operation of this engine compared to a gasoline engine.

What did we see?

• 4 Stroke Cycle

• Intake + Exhaust Valve

• No Spark Plug

• Fuel Injector in the middle

So how does it work?

• Compression-Ignition Engine

• This engine compresses air until it is hot enough to ignite the fuel

Multiple Choice

What part is going to start the power stroke on a diesel engine?

• Spark Plug

• Fuel Injector

• Glow Plug

• Turbocharger

Let's Break it down...

• A spark plug would not ignite diesel fuel

• If gasoline were used it would combust at the start of the compression stroke and make no power

• Diesel fuel is thick and hard to ignite

Fuel System

• Since the diesel fuel is thicker it needs to be forced into the engine using a mechanical fuel pump and nozzle (injector)

• Fuel is injected directly into the combustion chamber

• The engine uses a very high compression ratio increasing the air temp

• As soon as fuel is sprayed in it begins to burn.

Multiple Choice

On a gasoline engine air/fuel igniting on its own is known as?

• Knocking (Pinging)

• Misfires

• A rich mixture

• Engine Failure

Multiple Choice

Would it be safe to say that a diesel engine uses control knocking to ignite the air/fuel mixture?

• Yes

• No

Technically a diesel engine is constantly knocking

• As the air fuel burns the engine rattles and clatters

• Play diesel sounds here

Now what if the knocking becomes more than normal?

• If too much fuel ignites at one time the engine can produce a louder that normal noise

• This results in reduced power, fuel econmy, and engine life

Soot

• Soot is unburnt fuel from the engine

• Diesels will continue to spray fuel after the power stroke to keep the expansion smoother and quieter

• Too much soot is a sign of poor performance, efficiency, and lack of air.

• Also known as rolling coal

Open Ended

To wrap things up today for this portion of the lesson. Tell me one advantage of diesel fuel over gasoline fuel, and one disadvantage.

Open Ended

How does a diesel engine combustion process differ from of a gasoline engine?

Assignment: Examine the diesel fuel system.