Green Power with biomethane
Climate-friendly driving is not only possible with batteries, but also with gaseous fuels. More precisely with biomethane (CH4), which is obtained from organic waste and agricultural residues and offers a promising complement to the advancing e-mobility. The use of biomethane in the combustion engine reduces both CO2 emissions and the primary energy demand very significantly over the entire life cycle. An in-house development by IAV shows how a vehicle powered purely by methane can achieve a range of more than 900 km. The concept makes it possible to increase the efficiency of a biomethane-powered gasoline engine in a hybrid powertrain to over 45 percent while at the same time achieving the lowest possible pollutant and greenhouse gas emissions. IAV presented the study at the Aachen Colloquium 2020 on Sustainable Mobility.
Achieving the Paris climate protection targets is and will remain difficult as most sectors of the economy still predominantly use fossil fuels and emit environmentally harmful greenhouse gases. What is needed are not only innovative drive and mobility concepts, but also climate-friendly substitutes for oil and coal. One option is biomass as an important source of renewable energy.
Resource-saving biomethane is produced by fermenting animal manure as well as waste and residual materials from household, forestry and agriculture. Its combustion as a fuel in a vehicle releases only as much CO2 as the processed plants have bound during their growth.
Use of biomethane in the combustion engine
IAV has been developing technology solutions for forward-looking drive concepts for decades. This time IAV has designed a highly efficient hybrid with stoichiometrically driven combustion engine (ICE) for the use of methane. Among other technologies, the IAV “Metamax” study uses pre-chamber ignition as well as cooled low-pressure exhaust gas recirculation, which makes it possible to increase the effective efficiency of the gasoline engine at its best from 39 percent currently in series production to more than 45 percent.
At low ICE power demand, the electric motor is intended to power the vehicle, since the exhaust gas temperature in this operating range does not reach the required 550°C. However, this is absolutely necessary to enable a safe catalytic conversion of methane as well. At cold temperatures, the catalytic converter is electrically preheated before the ICE is started, so that it can convert from the first second on. In the serial/parallel hybrid system, the torque requirements on the ICE are reduced during strong acceleration. As a result, the ICE can be designed for higher efficiency right from the start and always run close to its sweet spot while running.
“Methane in itself already enables the very low raw emissions of pollutants in the ICE However, previous concepts still run on a small gasoline fear tank,” says Dr. Emanuel Binder, development engineer in IAV’s Advanced Powertrain Development department.
«We wanted to develop a vehicle concept suitable for everyday use that has a long range and requires methane only.»
— Development engineer in IAV's Advanced Powertrain Development department.
Lowest CO2 emissions over life cycle, low primary energy requirement
The biomethane is stored in special tanks in the rear of the vehicle at a pressure of 200 bar. The range of 920 km is mainly achieved by the 168-liter tank volume and the high system efficiency of ICE and hybrid components. Low-pressure port injection is also beneficial to the range.
As part of the study, IAV compared the biomethane drive concept with selected technologies such as battery-electric vehicle (BEV), plug-in hybrid electric vehicle (PHEV), hydrogen fuel cell (FCEV) and synthetic fuels (PtL) and examined them in terms of energy efficiency in the life cycle (cradle-to-grave). The result: From a life cycle perspective, a biomethane-fueled ICE on the road shows the best combination of low CO2 and low primary energy demand, because especially in the production of biomethane only a small number of conversion steps are required and the combustion properties of the green gas have a positive effecton ICE efficiency.
One thing is clear: no single drive type can serve all applications, markets and requirements, especially not when it comes to the amount of fuel or energy required. What is needed is an interplay of smart technologies and measures to make transport more sustainable – combustion engines remain an important part of this. When developing drive concepts, IAV not only focuses on the components but on the overall picture. Life-cycle considerations are therefore not at the end of the development process, but at the very beginning.
