ASE F1 Compressed Natural Gas Vehicles flashcards
ASE F1 Compressed Natural Gas Vehicles · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- CNG service pressure
- The rated storage pressure of a CNG system, commonly 3,600 psi for light-duty vehicles and 3,000 psi for many legacy systems, measured at a reference temperature.
- Methane flammability range
- Methane burns in air only between roughly 5% and 15% gas by volume, a narrower window than gasoline vapor, which affects leak and venting safety decisions.
- CNG vapor density
- CNG is lighter than air with a specific gravity near 0.55 to 0.6, so released gas rises and disperses outdoors rather than pooling at ground level.
- NFPA 52 scope
- The standard covering vehicular CNG fuel system installation, operation, and maintenance, including requirements for components, venting, and fueling facility safety.
- FMVSS 304
- The federal motor vehicle safety standard governing compressed natural gas fuel system integrity, addressing crash performance and component requirements for CNG vehicles.
- Type 1 cylinder
- A CNG storage cylinder constructed entirely of metal, with no composite reinforcement, commonly used in older or heavy-duty applications.
- Type 4 cylinder
- A CNG cylinder with a non-metal plastic liner fully wrapped with composite fiber, giving the lowest weight but requiring careful handling and inspection.
- Cylinder service life
- The manufacturer-specified maximum age, often 15 to 20 years, after which a CNG cylinder must be removed from service regardless of condition.
- In-tank solenoid valve
- An electrically operated valve at the cylinder outlet that opens only when powered, automatically isolating the cylinder when the ignition is off or a fault occurs.
- Pressure relief device
- A cylinder safety device that vents contents on overpressure or excessive temperature, using a fusible plug, burst disc, or thermally activated frangible element.
- Cylinder check valve
- A one-way valve that permits gas to enter the cylinder during filling but prevents backflow into the fill line when the nozzle is disconnected.
- Cone-and-thread fitting
- A high-pressure CNG connection in which a cone-shaped fitting seats into a matching cone, sealed by metal-to-metal contact and tightened to a specified torque.
- Tube bend radius
- The minimum allowable curvature for a rigid CNG line; exceeding it kinks or crushes the tube, restricting flow and creating a fatigue crack point.
- High-pressure filter
- A component downstream of the cylinders that traps particulate debris and oil carryover before gas reaches the regulator and injectors, protecting them from clogging.
- Line clamping and routing
- CNG lines must be supported and routed away from heat, moving parts, and abrasion points to prevent vibration fatigue, chafing, and heat damage.
- Two-stage regulator
- A regulator that reduces cylinder pressure to an intermediate level and then to final delivery pressure, improving stability and reducing icing and pressure droop.
- Joule-Thomson cooling
- The temperature drop that occurs as high-pressure gas expands through the regulator, which can frost components and requires coolant heating or design compensation.
- Manifold reference line
- A hose connecting the regulator to intake manifold pressure so delivery pressure tracks manifold pressure, keeping the injector pressure differential constant.
- Low-pressure lockoff valve
- A solenoid that opens only when the ECM commands fuel and the engine is cranking or running, adding a safety shutoff in the low-pressure section.
- Stoichiometric ratio for methane
- The chemically correct air/fuel mass ratio for methane, about 17.2:1, compared with roughly 14.7:1 for gasoline, used by the ECM for fueling calculations.
- Gas injector pulse width
- The opening duration commanded by the ECM; delivered fuel mass depends on pulse width, injector flow rating, and the pressure differential across the injector.
- Fuel trim interpretation
- Positive long-term trims indicate the ECM is adding fuel to correct a lean condition, such as a vacuum leak or restricted gas delivery; negative trims indicate rich operation.
- Mixer fuel system
- A CNG metering design that uses venturi vacuum in the intake airflow to draw gas, requiring careful intake sealing because lean conditions increase backfire risk.
- Methane octane rating
- Methane has a high research octane number, roughly 120 to 130, allowing higher compression ratios than gasoline but requiring matching spark timing and knock control.
- CNG ignition energy demand
- Methane's high ignition temperature and lean-burn characteristics demand strong coils and correct plug gaps; weak ignition shows up first as misfire on CNG.
- Spark plug heat range
- The plug's ability to shed heat; an incorrect range on a CNG engine can cause fouling when too cold or pre-ignition when too hot.
- NGV1 receptacle
- The light-duty CNG fueling connection with an integral check valve that accepts the dispenser nozzle and seals when the nozzle is removed.
- Defueling procedure
- The approved method of removing gas from a CNG vehicle using a defueling system that vents to a safe outdoor location, never into an enclosed space.
- Combustible gas detector
- A calibrated electronic instrument used to locate methane leaks by measuring combustible gas concentration, preferred over leak solution in confined or poorly ventilated areas.
- Cylinder label verification
- Checking the cylinder label for manufacture date, service pressure, and requalification interval; an expired cylinder must be removed from service.
- Supply versus delivery pressure
- Supply pressure is measured at the regulator inlet from the cylinders; delivery pressure is the regulated low pressure to the injectors, and comparing both isolates faults.
- Injector contribution test
- A diagnostic that disables or measures each cylinder in turn to identify a weak or clogged gas injector causing misfire or lean codes on one cylinder.