Why Do Pressure Gauges Need R110 Approval for CNG and LNG Applications?

Pressure gauges used in compressed natural gas (CNG) and liquefied natural gas (LNG) vehicle applications must meet the appropriate safety requirements for the markets where those vehicles will be sold. For natural gas vehicles (NGVs) sold in Europe, this includes compliance with United Nations Economic Commission for Europe Regulation No. 110 (UN/ECE R110).

Safety is especially important in CNG and LNG systems because natural gas is stored and transported under demanding pressure and temperature conditions. Pressure measurement instruments must be able to perform reliably under these conditions and meet the applicable regulatory requirements.

Approval requirements also vary by region. The requirements for cars and trucks in the U.S., for example, differ from those for vehicles manufactured for the European market. In this article, you will learn how CNG and LNG vehicles operate, some of the challenges associated with these fuels and why R110 approval is important when selecting pressure gauges for NGVs sold in Europe.

What are CNG and LNG-powered vehicles?

CNG and LNG-powered vehicles use natural gas, primarily methane, as an alternative to traditional gasoline or diesel fuel. CNG is commonly used in passenger vehicles, while LNG can be well suited for larger trucks that need to travel longer distances.

Although both fuels come from natural gas, the way they are stored and used creates different operating considerations.

What Is compressed natural gas (CNG)?

Compressed natural gas (CNG) is natural gas that is compressed and stored in high-pressure cylinders for use as a vehicle fuel. It is a clear, odorless and non-corrosive fuel that can provide an alternative to traditional gasoline or diesel.

Advancements in fuel storage technology have helped support the use of CNG in vehicles such as sedans, SUVs and pickup trucks. Some reasons CNG is used as an alternative vehicle fuel include:

• Cost: CNG can provide an economical alternative to conventional vehicle fuels.
• Emissions: Natural gas can offer emissions advantages compared with conventional gasoline or diesel, depending on the vehicle and application.
• Fueling availability: CNG refueling infrastructure allows appropriately equipped vehicles to refuel at dedicated natural gas fueling stations.

How do CNG vehicles work?

• CNG vehicles use spark-ignited combustion engines that operate similarly to gasoline engines, but the fuel is stored and delivered as high-pressure natural gas. 

• Natural gas is stored in a high-pressure fuel tank and transferred through the vehicle's fuel lines. A pressure regulator reduces the gas pressure to a level appropriate for the engine's fuel injection system.

• The fuel then enters the intake manifold or combustion chamber, where it mixes with air, is compressed and is ignited by a spark plug.

What are the risks of CNG vehicles?

CNG systems must be designed to safely contain and control high-pressure natural gas because leaks or component failures can create fire hazards.

Extreme temperatures can cause fuel and system components to expand or contract, which can affect system performance. Manufacturers must therefore consider the conditions that CNG components will experience throughout the vehicle's operation.

Figure 1. Potential CNG vehicle fire risks.

What is liquefied natural gas (LNG)?

Liquefied natural gas (LNG) is natural gas that has been cooled to approximately -162 °C (-260 °F), converting it into a cryogenic liquid.

Like CNG, LNG consists primarily of methane. The key difference is its physical state and storage method. Because LNG is stored as a dense liquid, an LNG tank can hold more fuel in a given volume than a comparable CNG storage system. This higher energy density makes LNG useful for larger vehicles, particularly trucks that need to travel long distances.

Figure 2. Example of an LNG storage and fueling station.

What are the challenges of using LNG?

LNG requires careful handling because it must remain at cryogenic temperatures and changes in temperature can cause the liquid to vaporize and increase tank pressure.

If an LNG storage system is not properly managed, heat entering the tank can cause some of the LNG to vaporize. Without appropriate pressure management and ventilation, pressure can build inside the tank and create a potential safety hazard.

Other LNG-related hazards must also be considered when designing and operating these systems.

Figure 3. Potential LNG safety risks.

What is UN/ECE Regulation No. 110 (R110)?

UN/ECE Regulation No. 110, commonly called R110, establishes requirements for the approval of specific components and vehicles that use CNG and/or LNG in their propulsion systems.

The regulation addresses the approval of:

• Specific components used in the propulsion systems of CNG and/or LNG-powered vehicles.
• Vehicles equipped with approved CNG and/or LNG components in their propulsion systems.

For pressure gauges used as covered components in CNG or LNG vehicle systems subject to R110, the appropriate R110 approval is required.

Why is testing pressure gauges with natural gas important?

Testing a pressure gauge with natural gas can help identify very small leak paths that may not be apparent when testing only with liquids such as water or oil.

The 8008S and 8009S gauges have been tested with natural gas at pressures up to 400% of scale working pressure. This testing helps confirm that wetted components do not contain micro-cracks that could allow gas to escape.

This distinction is important because liquids such as water or oil may temporarily seal extremely small cracks and hold pressure where a gas could potentially seep through.

What other conditions are evaluated for R110 pressure gauges?

R110 testing evaluates a gauge's ability to perform under conditions representative of CNG and LNG vehicle service, including pressure, leakage, vibration and environmental exposure.

The gauges are tested for external leakage while under pressure. Because gauges installed on vehicles can experience continuous vibration, testing also helps verify that they can withstand the vibration frequencies they may encounter during operation.

For applications where components may be exposed to corrosive environments, including vehicles or equipment operating near coastal areas, salt spray exposure is another consideration. Using 304 or 316L stainless steel components can provide corrosion resistance for these demanding environments.

Ready to learn more?

Selecting the right pressure gauge for a CNG or LNG application requires considering pressure requirements, operating conditions, materials and applicable regulatory approvals. Check out related pressure gauge resources

You can also contact Ashcroft to talk with an industry expert and get answers to your pressure gauge questions.

For information about pressure and temperature measurement in another alternative energy application, download the Pressure and Temperature Instrumentation in Hydrogen Systems guide.