Compressed Natural Gas (CNG) Vehicles Flashcards

What is the main component of compressed natural gas?

Answer: Methane

CNG is predominantly methane (CH4), the simplest hydrocarbon.

Compared to LPG (propane), how does CNG behave if released in an enclosed garage?

Answer: It rises and may need high-mounted detectors and ceiling ventilation

Methane is lighter than air, so detection and ventilation must address the upper area of the space.

A technician smells the mercaptan odor near a CNG vehicle in the shop. The correct action is to:

Answer: Evacuate, eliminate ignition sources, and ventilate the area

A detected leak requires removing ignition sources, ventilating, and isolating the fuel supply before repair.

What is one advantage of CNG regarding engine oil and maintenance?

Answer: Cleaner combustion can reduce oil contamination and deposits

CNG's clean burn produces fewer combustion byproducts that contaminate oil and form deposits.

On a dedicated CNG vehicle, the energy density issue means tanks are:

Answer: Larger and heavier to store enough energy for comparable range

Because CNG has lower energy per unit volume, vehicles need large high-pressure cylinders to achieve useful range.

Which standard governs CNG fuel system installation and inspection in many U.S. applications?

Answer: NFPA 52 (Vehicular Natural Gas Fuel Systems Code)

NFPA 52 covers the design, installation, and inspection of vehicular natural gas fuel systems.

When defueling a CNG vehicle for major repair, the gas should be:

Answer: Vented or recovered safely outdoors away from ignition sources

Defueling must occur in a controlled outdoor area, away from ignition, using approved venting or recovery equipment.