FEDERAL-MOGUL explains how modern pistons have evolved to meet the demands of greater durability, less fuel consumption and reduced emissions.
For more than a hundred years, diesel and petrol engines have remained significantly different technologies. Today, the need for CO2 reduction is bringing them together by adopting highly sophisticated direct injection systems with closed loop electronic control, high-pressure turbocharging and/or supercharging and fewer cylinders.
Pistons must endure the most aggressive forces, amongst the highest temperatures and the most dramatic thermal cycles of any engine component. They must be light to reduce the loads and losses due to their reciprocating movement and to contribute to overall vehicle weight reduction. Naturally, there can be no compromise on durability or reliability, which must also continue to advance.
The award-winning Monosteel® piston has become industry standard for heavy-duty diesel vehicle applications, with more than 3.5 million pistons produced to date. The Magnum Monosteel®, advances further by reducing piston mass by up to 7% and introducing a unique, “double-band” piston skirt that reduces friction by up to 17%.
Reducing friction and improving the wear resistance of pistons are particularly important in highly-boosted petrol engines. By using a coating comprised of solid lubricants, Federal-Mogul’s new Nüral EcoTough® pistons have demonstrated a reduction in friction of up to 18% combined with a substantial reduction in wear. They provide immediate improvements in fuel consumption, emissions and durability whilst extracting more performance from smaller engines creating a dramatic increase in combustion temperatures.
Nüral® pistons are designed in conjunction with the leading European vehicle and engine manufacturers and include optimised cooling gallery positions, making them ideal for high specific output turbocharged diesel engines.
For commercial vehicle applications, Federal-Mogul has developed a unique and highly efficient cooling concept applying highly flexible cooling galleries in terms of size and shape. Positioned close to the most critical areas, they allow more heat to be removed from the critical combustion chamber area and top-ring groove.
In high-performance, heavily downsized diesel engines, high-pressure turbocharging and new fuelling strategies, piston temperatures are pushing beyond 400°C and cylinder pressures to over 200 bar for cars, beyond 250 bar for heavy-duty trucks.
Federal-Mogul’s engineers have identified that failures of conventional piston bowls in this highly aggressive environment can be traced to the presence of silicon particles in the aluminium. By re-melting the alloy around the rim of the bowl, the silicon particles can be reduced to only one tenth of their previous size, substantially increasing the strength and durability of the piston rim.
The DuraBowl® piston uses this technique to increase service life between four and seven times compared with a conventional cast piston, allowing engine designers to continue to drive up efficiency to reduce fuel consumption and CO² emissions.
FITTING RIGHT IN
Another substantial challenge is ensuring a good fit within the cylinder at all loads and temperatures. The oval skirt shape of Federal-Mogul’s Nüral Elastoval® piston ensures optimum compliance of the piston skirt, allowing it to adapt as the load changes. Coupled with high geometric stability and minimized piston weight, this provides Elastoval® pistons with increased durability, superior anti-seizure properties, and reduced friction.