AP7 - Efficiency improvement of vehicles

Extremely low carbon dioxide emissions applying biogas

This working package is a part of the overall project “Virtual Biogas” and its objective is to increase the cruising range of gas-propelled vehicles by increasing the efficiency of the whole propulsion system. In doing so, the application of upgraded biogas (biomethane) in the internal combustion engines of passenger cars will be researched. About 50% of these engines are based on the Otto-principle (this means on induced ignition). Therefore, these engines have the best preconditions for switching to methane as a fuel.

A goal of this project is to further improve the mean efficiency of the drivetrain of a gas-propelled passenger car during a real and a statutory driving cycle. Driving cycle efficiencies similar to Diesel-engines in the range of 22-25% have to be achieved. Therefore, also the maximum engine efficiencies will have to be similar to Diesel-engines in a range of 38%. Additionally, it will be analysed whether and to which extent a further augmentation of the power density (mean engine pressure of higher than 25bar during gas operation using turbo-supercharging) together with a downsizing of the engine displacement and a hybridisation of the drivetrain is possible.

Drive cycle simulations will be used to analyse if mean drive cycle efficiencies exceeding 30% are possible applying the named concepts. Due to the reduced carbon content of methane as a fuel, the local carbon dioxide emission could be cut by 50% compared to gasoline-powered vehicles depending on the vehicle category! The lower carbon dioxide turnover qualifies these technology components to enhance the biogenous fuel ratio in the individual transportation sector. Moreover, the high yield of biogas fuel per acreage and the high engine efficiency lead to the highest protection of infrastructure and environment.

The results of these examinations reveal that the carbon dioxide emission of one middle-class passenger car can be decreased to lower than 80g/km, if a turbo-charged gas engine with direct-injection and hybridisation is applied. Typical cruising ranges of modern gasoline-powered cars can be reached if such a drivetrain is applied.

In order to analyse the influence of varying gas quality on the combustion several biogas mixtures have been combusted in a research engine. Using engine process simulation tools the results of these experiments have been transferred to a vehicle engine and subsequently the whole propulsion system has been simulated. With this approach the carbon dioxide emission and the cruising range potential of biogas-powered hybrid vehicles have been determined. In the following steps the potentials of the newly developed gas-direct-injection-technology will be compared to conventional engine technology (regarding efficiency/CO2 potential, pollutant emissions and downstream exhaust cleaning techniques).

The following two are the main scientific targets:
  • Verification and indemnification that upgraded biogas is a suitable fuel for future efficiency-optimised gas engines with direct gas injection. In order to analyse the influence of the specific properties of upgraded biogas on the combustion the tested gas quality is selectively varied. Namely, the ratio of methane to carbon dioxide is varied, while a higher amount of carbon dioxide stands for a less intensive biogas upgrading step (lower production costs). The variation of the gas quality is done even beyond the limits given by the standard for grid injection, ÖVGW G31.
  • The efficiency of the drivetrain shall be increased together with an improvement of the vehicle cruising range. The current gas engines using gas injection only in the inlet manifold (not directly in the cylinder) suffer significantly from low cruising ranges. Therefore, a considerable improved efficiency of the propulsion system significantly contributes to the customer’s acceptance for gas-powered vehicles. The improvement of the efficiency of the internal combustion engine mainly is attributed to the alteration of the gas injection from the air manifold to the actual cylinder and to a further optimisation of the direct-injection-combustion process.