There is also further potential to exploit the high knocking resistance of methane by specifically engineering the engine design. CNG engines used in today's passenger vehicles are typically only lightly-modified gasoline engines and therefore not optimized for operation with methane. The EU GasOn project started work in 2015 to exploit the potential of methane, researchers from ETH Zurich and Empa also participated in a work package led by Volkswagen Group Research.
An engine optimized to run on CNGA highly efficient combustion process was developed and used in the design of a 2 liter CNG engine: A lean gas mixture is first ignited in a thimble-sized, flow-controlled prechamber. In the ETH-Laboratory for Aerothermochemistry and Combustion Systems, fundamental experiments on the ignition behavior in the pre-chamber and the resulting hot gas expanding into the main combustion chamber were investigated. With the help of this data, mathmatical models were further developed in order to be able to characterize the processes in detail by means of computer simulations.
The results allowed Volkswagen Group Research to optimize the design of the prechamber and main combustion chamber. At Empa, an engine has been designed to allow further investigation of the combustion characteristics. An engine management system developed by the Institute for Dynamic Systems and Control Technology at the ETH Zurich was used. This system provides overall engine control and allows adaptation of operating conditions according to research findings.
Efficiency record for passenger car enginesCompared with previous designs the new CNG engine with pre-chamber combustion leads to the fuel consumption saving of about 20% (based on the WLTP standard consumption of a mid-range car). The peak efficiency of the new engine design was over 45%, with efficiencies of over 40% recorded over wider operating conditions. Such values are currently only achieved by significantly larger engines, such as those found in commercial vehicles, in fixed installations or in marine applications. This is a new record for car engine efficiency. By comparison, gasoline engines have maximum efficiencies of 35 to 40% across their optimal working range. In the GasOn project, the engine exhaust post-treatment has not yet been processed; there is still a need for research here due to the lean burning process.
Overall, it has been shown that a relatively small CNG engines can achieve similar efficiencies to much larger diesel engines. They also run easily on any fuel ratio made up of renewable biogenic and synthetic methane, achieving very low CO2 emissions. The participating vehicle manufacturers are now clarifying how the results of the GasOn project can be transferred to production vehicles.