Introduction · “YOU HAVE TO KNOW THE PAST TO UNDERSTAND THE PRESENT.” - CARL SAGAN

Introduction “YOU HAVE TO KNOW THE PAST TO UNDERSTAND THE PRESENT.” - CARL SAGAN Moving towards an all-electric future, innovations in engine design are required to extend the useful life of the internal combustion engine. As hybrid and full-electric propulsion systems are still evolving towards “mass electrification”, innovations like Mercedes newest M139 engine will extend the life of the internal combustion engine by reducing global emissions and conserving resources.3 The M139 is the world’s most powerful four cylinder, producing 421 horsepower out of a series production turbo-charged 2.0 liter engine. At the heart of this efficient engine is a chill-cast aluminum crankcase, engineered for thermal and volumetric efficiency, strength, rigidity, and weight savings, which wouldn’t be possible without the modern all-aluminum engine.4 Historically, cast iron was selected for use in engines due to low cost, castability, and durability. Cast iron or steel was even used for pistons in iron blocks up and through WWII, although high engine temperatures would cause the material to soften. W.O. Bentley, a British engineer who designed engines for automobiles and aircraft, as well as founder of Bentley Motors Limited, came to the realization that even though aluminum has a lower melting point, its much higher thermal conductivity could help keep the pistons cool enough to prevent softening. Besides providing cylinder sealing and oil control, piston rings are responsible for transferring heat away from the piston through the cylinder wall and into the coolant, to keep the piston from melting down.5 With 70%6 of the combustion chamber heat transferring from the piston through the top (compression) piston ring to the cylinder bores, increased end gaps must be provided to prevent ring-butting in high performance engines with iron bores due to increased temperatures. Most modern engines also employ piston squirters to aide in piston cooling and control expansion rates while maintaining tight piston to cylinder clearances for quiet operation. An all-aluminum engine will provide a more efficient path to transfer the heat away from the pistons and rings, supporting elevated pressure and temperature levels required of modern, downsized and turbocharged high performance engines, like the M139.7 The higher thermal conductivity of aluminum over cast iron or steel provides for lower cylinder surface temperatures, reducing hot spots and the likelihood of self-ignition.8 3 Extending the ICE Age. SAE International July/August 2019. 4 Mercedes AMG extracts world-record power from new four-cylinder engine. SAE International July/August 2019. 5 Piston to Cylinder Wall Heat Paths. Cameron, Kevin. Cycle World. https://www.cycleworld.com/2013/12/05/ask- kevin-why-rings-are-the-highest-flowing-heat-path-from-piston-to-cylinder-wall/ 6 Piston and Piston Rings. University of Windsor. https://courses.washington.edu/engr100/Section_Wei/engine/UofWindsorManual/Piston%20and%20Piston%20Rin gs.htm 7 Heat Transfer Versus PIston-Ring Endgap. Hot Rod Network. https://www.hotrod.com/articles/heat-transfer-versus- piston-ring-endgap/ 8 Introduction to Internal Combustion Engines. Stone, Richard. SAE International. Pg 404, 431-432. LN Engineering Technical Library. Copyright ©2019 LN Engineering LLC