ASE Compressed Natural Gas (CNG) Vehicles 3

Question 1

Compared to gasoline, CNG has a higher octane rating of approximately what value?

Accepted Answer

120-130

Answer

CNG's effective octane rating of about 120-130 allows higher compression ratios and resists knock.

Question 2

Which exhaust emission is significantly reduced when an engine runs on CNG instead of gasoline?

Accepted Answer

Carbon monoxide and particulates

Answer

CNG combustion produces lower CO and particulate emissions due to its clean-burning, simple molecular structure.

Question 3

A bi-fuel CNG vehicle is one that:

Accepted Answer

Can run on either CNG or gasoline from separate tanks

Answer

A bi-fuel vehicle has both CNG and gasoline storage and can switch between the two fuels.

Question 4

Why might a CNG engine experience slightly reduced power compared to the same engine on gasoline?

Accepted Answer

Gaseous fuel displaces intake air, lowering volumetric efficiency

Answer

Because CNG enters as a gas it occupies cylinder volume that would otherwise hold air, reducing charge density and power.

Question 5

What type of fuel injector is typically used in a dedicated CNG engine?

Accepted Answer

Gaseous/low-pressure port injector

Answer

CNG systems use gaseous fuel injectors designed to meter low-pressure natural gas into the intake ports.

ASE Practice Test