Advanced Fueling Method to Achieve Full Fill for Natural Gas Vehicles

Advanced fueling method to achieve safe and consistent full fills for CNG vehicles


Institute of Gas Technology dba Gas Technology Institute


Irvine, CA

Recipient Location


Senate District


Assembly District



Amount Spent



Project Status

Projects Updates/The Results

The advanced fueling algorithm combined with wireless communication of data between the vehicle and dispenser demonstrated termination of all fills at nearly 100 percent full in every thermodynamically possible case. Further development should be focused around packaging the algorithm with wireless data transmitting hardware in dispensers and vehicles. Pre-cooling is necessary to achieve full fills in cases with high ambient temperature. GTI investigated a variety of potential hardware options, but additional research is needed to develop low cost pre-cooling for CNG stations. The final project report was accepted in February 2019. GTI is using results from this project to work with CSA Group, a leading codes and standards organization for NGVs, to write a guidance document on developing new standards for safe full fills and fueling algorithms.[br /]

The Issue

Safely and accurately achieving a full fill in a compressed natural gas (CNG) natural gas vehicle (NGV) is a technical challenge the NGV industry continues to struggle with when using a fast-fill CNG dispenser. The inaccuracies that cause under filling, largely the result of ambient temperature and heat generation within a CNG cylinder as it is filled with high pressure gas, are typically compensated for by slightly over pressurizing a cylinder. The shortcomings of this approach are a significant obstacle to optimizing vehicle range and ensuring the safety, reliability, and consistency of CNG dispensers.

Project Innovation

Gas Technology Institute (GTI) developed a gas characterization technique and fueling algorithm that uses communication between NGVs and CNG dispensers to identify tank volume, pressure, and temperature prior to filling. The algorithm improves consistency and safety of natural gas vehicle fueling by validating when the vehicle is near the full fill target. GTI also performed fueling simulations to evaluate current state-of-the-art fueling methods and improved fueling algorithms developed using the characterization technique. Using an environmental test chamber and a commercial heavy-duty CNG storage system, GTI tested the improved fueling algorithm and validated its benefits under a variety of real world conditions. GTI also investigated pre-cooling strategies that would be needed to achieve full fills at higher ambient temperatures. Addressing these issues and developing a solution that can be deployed across the NGV industry can improve the competitiveness of low emission, heavy-duty NGVs.

Project Benefits

This project addressed major industry concerns with fast fill CNG stations by improving their effectiveness in achieving full fills. Under filling CNG vehicles leads to reduced operating range and the need for storage compensation with larger storage volumes. Addressing these concerns can increase adoption rates of natural gas vehicles in key market segments that rely on fast fill stations (e.g., goods movement). Heavy-duty vehicles in this sector are predominantly diesel and represent a major source of greenhouse gas and pollutant emissions in California. Displacing these vehicles with cleaner natural gas options will improve air quality and reduce the carbon impact of the transportation sector.

Consumer Appeal

Consumer Appeal

Heavy-duty natural gas vehicles with a 20 percent under fill can result in a 30 gasoline gallon equivalent of underutilized fuel capacity, which directly translates to reduced maximum range. Consistent full fills will effectively increase the maximum range of natural gas vehicles and improve their competitiveness to diesel vehicles.

Lower Costs

Lower Costs

Achieving consistent full fills improves the economics of natural gas vehicle fleet operations by maximizing vehicle range and reducing frequency of refueling. CNG on-board storage systems are typically oversized to compensate for under filling. The capital costs for on-board storage systems can be reduced by 10 percent ($5,000 per vehicle for some heavy-duty vehicles) if oversizing can be avoided without losing range.

Increase Safety

Increase Safety

Real world testing of the fueling algorithm demonstrated termination of all fills at nearly 100 percent full, with only one case of slight overfill within the error of the pressure transmitter. Standardizing this fueling algorithm for the CNG industry can result in safer fills and a foundation for future pre-cooling technologies to assist in achieving full fills at high ambient temperatures.

Key Project Members

Project Member

Jason Stair

Principal Engineer



Agility Fuel Solutions


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