Methane as a Vehicle Fuel
This project aims to develop a technical solution for individual mobility with
- a reduced dependency on crude oil by the use of the alternative fuel natural gas or purified bio-gas
- and a reduced environmental impact (greenhouse gases and pollutant emissions)
without sacrificing the vehicle's performance.
Natural gas or biogas consists mainly of methane (CH4). One important difference of bio-methane to other bio-fuels is that it can be produced very efficiently from almost any biogenic source (green waste, wood, liquid manure) and it does not compete with food production.
Methane is a color- and odorless fuel and very well suited to be used in spark ignited internal combustion engines. The octane number (RON) of about 130 for pure methane is much higher then the one of gasoline. This enables the implementation of high compression ratios and/or enhanced downsizing/boosting concepts. Related to the chemical energy content, methane produces about 25% less CO2 emissions compared to gasoline or diesel fuel. Methane has a simpler oxidation chemistry than the much more complex liquid fossil fuels. This leads usually to lower pollutant emissions. A major challenge for methane vehicles is the catalytic oxidation of the unburned hydrocarbons because they consist mainly from the chemically stable methane.
Methane is lighter than air, vehicles can safely be parked in basement garages for example. Methane is generally a very safe fuel. It is stored in pressurized cylinders under 200 bar filling pressure. Such cylinders are designed in a way that they will not burst in an accident. The worst accident case is where the piping is cutted off. In this case, a flame would burn very locally in contrast to a gasoline accident where the fuel tank can leak which can lead to a much more serious incident.
Infrastructure and Range
In many countries, a methane filling infrastructure exists and the natural gas industry invests in a good coverage. In Germany, the gas industry's goal is to operate 1.000 filling stations. In Switzerland, 100 filling stations will be available soon. In a conventional mid-size passenger car, about 20 kg of methane (CNG: Compressed Natural Gas) can be stored in underfloor bottles with nowadays storage technology at 200 bar filling pressure. This is roughly equal to the chemical energy content of 30 liters gasoline. To achieve a sufficient range, the vehicle has obviously to be as efficient as possible. With today's solutions, available passenger CNG cars or light commercial CNG vehicles achieve a range of around 300 km which is sufficient for many applications. However, one major goal in the R&D of methane vehicles is the enhancement of the range to weaken their disadvantage compared with liquid fuel driven vehicles. An increased range can be achieved with four different measures:
- An increased storage volume onboard the vehicle
- An increased filling pressure
- An increased powertrain efficiency (e.g. by downsizing and/or hybrid conceps)
- A decrease of the vehicle's energy need (e.g. by mass and drag reduction)
- The modification of the fuel (e.g. hydrogen-enrichment in the filling station or with a on-board reformer)
The CLEVER project focuses on point 3.