Dedicated gas vehicles use a spark ignition engine that runs on 100% gas. These engines produce significantly lower noise, particulate matter and NOx emissions than their diesel counterparts. Dedicated gas vehicles can store their fuel in compressed or liquefied form, and when operated on 100% biomethane they offer around a 60% - 75% well-to-wheel CO2 emission savings compared to their diesel equivalents.
Due to engine size constraints in European vehicles, dedicated gas vehicles are available up to circa 340 hp (~26 tonne GVW). Since the vehicles are capable of operating on gas fuel only, their operation needs to be restricted to within range of appropriate refuelling infrastructure. Dedicated gas vehicle manufacturers offer various tank capacity options to extend the vehicle range to meet customer requirements.
Bi-fuel gas and petrol
Some dedicated gas vehicles retain a petrol refuelling system to allow the vehicle to switch between petrol and gaseous fuels. These are known as bi-fuel vehicles. Bi-fuel variants are typically available for light duty gas vehicles. Bi-fuel operation alleviates the range constraints of operating a dedicated gas vehicle in areas of poor refuelling station availability. Dependent on the vehicle design, some vehicles switch to the petrol system once the gas fuel has run out, allowing a small capacity ‘emergency’ petrol supply to become available. Other vehicles have larger tanks so that long distances can be covered in petrol mode.
Dual fuel vehicles simultaneously combust diesel and gas in a compression ignition engine with diesel providing pilot ignition of the gaseous fuel. The vehicles retain a similar efficiency to a diesel vehicle and emission savings can be realised from the lower carbon content of natural gas compared to diesel. Dual fuel vehicles can also offer an improvement in air quality emissions. Further CO2 emission savings are available from the use of renewable fuels, such as biomethane or biodiesel.
The quantity of gas utilisation in the engine increases with engine speed and load. Therefore dual fuel vehicles are most suited to haulage operations. The ability to run on 100% diesel fuel is also retained if a gas station is not available, meaning these vehicles can operate in locations where gas refuelling stations are scarce.