At the 2017 IAA motor show in Frankfurt, Federal-Mogul Powertrain plans to reveal advances aimed at cooling the valves of downsized boosted engines via significant heat transfer. For exhaust valve head alloys, every 20°C reduction in temperature negates the need for an upgrade to the next, more expensive alloy specification.
Gian Maria Olivetti, Chief Technology Officer, explained at the company’s Burscheid facility north-east of Cologne: “The extreme valve temperatures experienced on today’s highly boosted downsized engines can lead to reduced valve fatigue life and critical valve guide and stem seal temperatures, resulting in the need for expensive valve steel alloys. If late ignition timing is used to reduce knock and enrichment is protecting components from critical temperatures, CO2 emissions are increased."
He said reducing the valve head temperatures helps to eliminate these issues. The company has developed new production-ready solutions for valve seats and guides, designed to deliver improved thermal conductivity suitable for series production.
They are HTC (High Thermal Conductivity) materials and TIM (Thermal Interface Material) coating to reduce valve head temperatures by up to 70°C, allowing improved combustion and lower emissions. HTC can also contribute to obtaining a more even circumferential temperature distribution on the valve seat insert and surrounding cylinder head material. By doing so, local hot spots can be avoided, so reducing wear reduction and temperature-related distortion.
Olivetti detailed the advances made by Federal-Mogul, stating that the seat insert is the primary heat path from the valve head into the cylinder head cooling jacket: “By conducting more heat away from the valve head, the new seat materials reduce the temperature in the hottest part of the combustion chamber and lower the gas temperature at the end of the compression stroke.”
This improves knock resistance and facilitates a wider range of ignition advance to enable optimization of combustion. A bonus is that the materials also contribute to CO2 emissions reduction by eliminating the need for fuel enrichment for cooling.
As the valve guide is the main heat path from the valve stem to the cylinder head, by conducting more heat away from the stem, the new valve guide material has been developed to reduce local temperatures below the critical thresholds at which the valve stem seals and lubricating oil begin to break down.
At Burscheid, tests involving “highly rated turbocharged gasoline engines” using a combination of HTC and TIM technologies are stated by Federal-Mogul to have reduced peak inlet valve head temperatures by between 26ºC and 32°C. The improvement in exhaust valve head temperatures was even greater; on a solid valve the peak was reduced by up to 70°C and on a hollow, sodium-filled valve, by up to 67°C.
The test results have been used to correlate predictions from the company’s advanced thermal simulation programs, allowing future applications to be accurately assessed and optimum materials selected, at the concept stage of a new engine’s creation.