Interest in natural gas fueled vehicles has grown substantially in recent years as people seek lower cost alternatives to gasoline and diesel. Currently natural gas powers about 112,000 vehicles in the United States and roughly 14.8 million vehicles worldwide.
Benefits of Natural Gas Vehicles
- Lower prices at the pump.
- 20-30% fewer Greenhouse Gas Emissions and 95% fewer tailpipe emissions vs. gasoline.
- Extended engine life.
- Domestically produced energy.
- Similar driving experience as conventional vehicles.
Challenges of Natural Gas Vehicles
- Substantial up-front vehicle costs.
- Limited places to refuel.
- Limited vehicle selection.
- Longer refueling times.
- Shorter driving range vs. gasoline or diesel.
Types of Natural Gas Vehicles
There are three basic types of natural gas vehicles (NGVs), each with their own unique applications:
These vehicles are designed to run only on natural gas. Dedicated NGVs may demonstrate better performance and have lower emissions than bi-fuel vehicles. Because dedicated NGVs only have one fuel tank, they aren't as heavy as bi-fuel NGVs and can offer more cargo capacity. One example of a light duty consumer vehicle with a dedicated CNG system is the Honda CNG Civic.
These vehicles have two separate fueling systems that enable them to run on either natural gas or gasoline. The main advantage of a bi-fuel vehicle is it can fully utilize cheaper CNG, yet it retains the flexibility of a gasoline system if CNG isn't available at a particular location. The current 2500 series light duty CNG trucks from Chevrolet, Dodge and Ford as well as nearly all of the CNG conversions (both factory and aftermarket) utilize bi-fuel systems.
These vehicles have fuel systems that run on a mixture of natural gas and diesel fuel. Generally these vehicles start on diesel then switch to a metered mix of natural gas and diesel. Dual-fuel vehicles are traditionally limited to heavy-duty applications such as over the road trucking and off-road diesel engines.
Regardless of the fueling system (dedicated, bi-fuel, dual-fuel), most NGVs offer similar levels of engine performance and fuel efficiency as their conventionally fueled counterpart. The driving range of NGVs generally is less than that of comparable conventional vehicles because of the lower energy density of natural gas. Extra storage tanks can increase range, but the additional weight can hinder vehicle performance and may displace payload capacity. Additional tanks can also significantly increase vehicle costs.
CNG Vehicle Components
As illustrated in the graphic above, a CNG vehicle has seven basic components. The CNG storage tank is generally located the trunk of a passenger car or in the bed of a light duty pickup. High pressure (3,600 psi) fuel lines deliver natural gas from the CNG tank through fuel filters to a pressure regulator. From there, lower pressure lines (150-700 psi) deliver natural gas to the engine. In the engine compartment fuel rails and injectors then meter and inject natural gas into the cylinders, just like in a conventional gasoline engine. An electronic control module manages the system and optimizes vehicle performance.
Figure 1. CNG vehicle components.
- CNG Fill receptacle (3,600 psi)
- CNG storage tank
- Dash mounted fuel selector switch
- High pressure fuel filters
- Pressure regulator
- Fuel rail and CNG injectors
- Electronic control module
Incremental Vehicle Costs
Incremental costs to purchase a new natural gas vehicle or to convert an existing vehicle can range from $10,000 to $20,000 for light duty cars and trucks. For heavy duty trucks, the costs can start at $50,000 and easily exceed $100,000. The US DOT's Alternative Fuels Data Center has an online tool to help you calculate annual fuel savings based on your mileage driven each year. With this number you can calculate how long it will take to 'repay' your incremental vehicle costs and begin to see a return on your CNG investment.
Prepared by David T. Messersmith, Extension Educator, Penn State Extension.