Week 3 Diesel Combustion Practice

Diesels have greater torsional vibration because of which reason?

• Lean Burn Combustion Chamber

• High Compression Ration

• High Fuel Pressure

• Lack of Internal Dampener

Tech A says the chemical reaction inside of a combustion chamber requires a fuel source. Tech B says it also requires Oxygen. Who is correct?

• Tech A

• Tech B

• Both Techs

• Neither Tech

During which engine stage does fuel react with oxygen to generate heat?

• Combustion

• Compression

• Induction

• Exhaust

A "Knock" is a premature ignition of which things?

• Fuel

• Air

• Neither A or B

• Both A and B

Tech A says Modern spark ignition engines run from either 8:1 to 11.5:1. Tech B says all engines run the same base amount of compression. Who is correct?

• Tech A

• Tech B

• Both techs

• Neither tech

Tech A says a spark ignition engines uses heat generated from the spark plugs to ignite the fuel. Tech B says glowplugs ignite fuel by making a spark of electricity jump a small electrode gap to initiate combustion. Who is correct?

• Tech A

• Tech B

• Both Techs

• Neither Tech

Answer explanation

Spark plugs start combustion by making a spark jump a gap, they don't generate ambient heat. Glowplugs are used on a diesel to help start it by increasing chamber temperatures, which make the fuel easier to ignite. A glowplugs body actually gets hot, a spark plugs isn't supposed to.

Tech A says a typical diesel engine will have a compression ration ranging from 15.5:1 to 17.5:1. Tech B says increasing compression ratio further than 23:1 generates even more power and increased engine efficiency by 25%.

• Tech A

• Tech B

• Both Techs

• Neither Tech

Answer explanation

Compression over 23:1 starts to lose gains made on compression power. This is because it becomes increasingly difficult to compress the air in the combustion chamber, creating larger pumping losses.

Tech A says diesel cranking compression is between 280 and 300psi. Tech B says low compression can create a hard start or no start situation. Who is correct?

• Tech A

• Tech B

• Both Techs

• Neither Tech

Answer explanation

Diesel ignition comes from compression. A drop in compression could mean that you are no longer able to start as easily, or in a worst case scenario, at all.

Which engine characteristics can influence the torque output an engine can deliver.

• Compression ratio

• Crankthrow leverage

• Cylinder Pressure

• All of these

What is the general cranking speed needed to start a diesel?

• 1000rpm

• 425rpm

• 125rpm

• 50rpm