Efficient Thermal Management

New two-phase cooling as a building block for compliance with RDE and Euro 7: Classic combustion engines must also make a contribution on the way to climate-neutral transport in 2050. By reducing thermal losses, fuel consumption and exhaust emissions can be further reduced.


The starting point for IAV’s development of a climate-friendly two-phase cooling system in the combustion chamber is the experience among engine developers that an engine does not work particularly efficiently if only little power is drawn off. In partial-load operation, fuel consumption is higher in relation to the energy generated, which leads to poorer efficiency.

This is why IAV has developed a two-phase cooling system in which the coolant temperature can be set between 80 and 200 degrees Celsius irrespective of the operating point. The closed circuit works with a mixture of water and ethanol as coolant. It evaporates in the engine, is expanded via a valve and condensed again in a radiator. A high-pressure pump feeds the medium into the engine at a pressure between one and 12 bar.

“The higher the pressure, the higher the temperature in the circuit”, says Thomas Arnold, team leader for combustion engine design and testing. “In this way, we can set the optimum pressure and thus also the most favorable wall temperature for combustion, depending on the operating point of the engine.” And we do this with great accuracy: The temperature difference between the wall and the coolant is between five and 20 Kelvin maximum.

Effizientes Thermo­management
Almost six percent less fuel consumption in the WLTC

While the highest possible wall temperature is desired in the partial load range, it should be as low as possible in the full load range to protect the components. This is also made possible by the new two-phase cooling system: “By reducing the pressure, we achieve significantly lower temperatures at full load than conventional cooling systems”, says Arnold. “This also increases the service life of the engine.”

To demonstrate the potential of two-phase cooling, IAV has equipped a conventional turbocharged 1.4-liter gasoline engine with the new technology. Tests show that this reduces fuel consumption in the WLTC by 5.6 percent. The lower coolant mass flow also contributes to this: Depending on the operating point, it is only one to two percent compared with conventional liquid cooling, meaning the coolant pump requires significantly less drive power.

Increased customer interest, new exhaust regulations

“With our comprehensive and long-standing engineering expertise, we are the right partner in the transformation”, says Matthias Krause, Head of the Internal Combustion Engine Design department.

«We not only provide our customers with the best solutions for efficient and flexible thermal management, but also ensure that everything functions optimally in the overall system.”»

Matthias Krause — Head of the Internal Combustion Engine Design department

Interest in the two-phase cooling system is currently receiving a boost from the increasing global requirements for exhaust gas emissions and CO2 output. In January 2021, for example, the second stage of the RDE test procedure for measuring real driving emissions will come into force. When the standard was introduced in September 2017, a vehicle was still allowed to emit 2.1 times the legally stipulated limit value. Next January, this conformity factor will drop again to 1.5.

“With the increasing demands on emissions, all reasonable savings potentials must be raised. Two-phase cooling can make a very good contribution in many engines”, says Krause.

Stay up to date

Subscribe to the newsletter