Technology

Dedicated natural gas vehicles (NGVs) are designed to run only on natural gas; bi-fuel NGVs have two separate fueling systems that enable the vehicle to use either natural gas or conventional fuel (gasoline or diesel).

In general, dedicated NGVs demonstrate better performance and have lower emissions than bi-fuel vehicles because their engines are optimized to run on natural gas. Since the vehicle does not have to carry two types of fuel, cargo capacity is increased and weight reduced. NGV horsepower, acceleration, and cruise speed are comparable with those of an equivalent conventionally fueled vehicle.

How NGVs Work

Light-duty natural gas vehicles work much like gasoline-powered vehicles with spark-ignited engines. The schematic below shows basic CNG fuel system components.

CNG enters the vehicle through the natural gas fill valve (A) and flows into high-pressure cylinders (B). When the engine requires natural gas, the gas leaves the cylinders and passes through the master manual shut-off valve (C).

The gas travels through the high-pressure fuel line (D) and enters the engine compartment. Gas enters the regulator (E), which reduces the gas pressure used for storage (up to 3,600 psi) to the required vehicle fuel injection system pressure. The natural gas solenoid valve (F) allows natural gas to pass from the regulator into the gas mixer or fuel injectors. The solenoid valve shuts off the natural gas when the engine is not running.

Natural gas mixed with air flows down through the carburetor or fuel-injection system (G) and enters the engine combustion chambers where it is burned to produce power, just like gasoline.

Schematic of a natural gas vehicle fueling system. Adapted from Compressed Natural Gas: A Suite of Tutorials. Courtesy of Thomason & Associates, Inc.

Source:  Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE)