Compressed Natural Gas (CNG) Vehicles Flashcards

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

Answer: 120-130

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

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

Answer: Carbon monoxide and particulates

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

A bi-fuel CNG vehicle is one that:

Answer: Can run on either CNG or gasoline from separate tanks

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

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

Answer: Gaseous fuel displaces intake air, lowering volumetric efficiency

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

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

Answer: Gaseous/low-pressure port injector

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

When refueling a CNG vehicle, the temperature compensation matters because:

Answer: Gas heats up during fast fill, so the tank may read full before reaching true capacity

Fast-fill heating raises pressure and can give a 'full' indication that drops as the gas cools (temperature/pressure relationship).

Which inspection is required on CNG cylinders at regular intervals per safety standards?

Answer: Visual inspection for damage, abrasion, and corrosion

Periodic visual inspection of CNG cylinders checks for cuts, gouges, corrosion, and impact damage that affect safety.