wear occurring at TDC and BDC due to a failure to maintain adequate hydrodynamic lubrication.44 Severe · wear manifests itself as

wear occurring at TDC and BDC due to a failure to maintain adequate hydrodynamic lubrication.44 Severe wear manifests itself as cylinder bore and piston scoring with the formation of grooves and ploughing of the aluminum matrix by the fractured silicon particles in the wear track.45 46 Tribology and the Al-Si Cylinder System Significant oil deposits on the cylinder surface fills uneven areas on the aluminum matrix, providing the required tribofilm for proper lubrication.47 Wear resistance mechanisms are reliant on the formation of this tribofilm and the subsequent formation of anti-wear additive films on the Al-Si matrix.48 An analysis of the cylinder surface anti-wear films shows that zinc (Zn), from ZDDP, and molybdenum (MoS2), from MoDTC friction modifiers, are deposited onto the load bearing silicon particles and the aluminum matrix that supports these particles. In normal operation, transfer of ferrous material from the piston skirt coating and rings to the bores allows for the formation of ZDDP wear pads on exposed Si particles. Formed under stress or high temperatures, these thermal- and tribo-films are thinnest at low temperatures, forming at temperatures as low as 25°C (77°F),49 reinforcing perhaps the reason we see more scoring with engines operated in colder climates or those driven primarily short distances. Where ZDDP forms through chemical desorption, moly films form glassy plates initiated through sliding motion that reduce friction and wear. Moly lowers the shear strength of the tribofilm resulting in a reduction in friction, enhancing the performance of ZDDP. In testing of Al-Si engines with start-stop, the presence of moly reduced the static coefficient of friction (μ) during restarts by 83.3% from 0.8-0.9 to 0.15.50 Changes in loads, speeds, or even lubricant temperatures have a direct affect on the characteristics of this tribofilm, as do the types and amounts of ZDDP and moly used.51 The thickness of these films varies depending on the concentration of ZDDP and moly, suggesting a ratio of 0.1 44 Failure of Piston in IC Engines: A Review. R.C. Singh, et. Al. International Journal of Modern Engineering Research, Volume 4/Issue 9 - Sept. 2014. 45 Combustion Engine Cylinder Liners Made of Al-Si Alloys. A.W. Orlowicz, et. Al. Archives of Foundry Engineering. DOI: 10.1515/afe-2015-0041. 46 Sliding wear behavior of eutectic Al-Si alloy under lubricated conditions: An investigation on the effect of ethanol (E85) addition. Victor Vimalrajan Francis. University of Windsor. 47 Friction and Wear of Tribo-Elements in Power Producing Units For IC Engines - A Review. Roop Lal, et al. International Journal of Engineering Trends and Technology - Vol 14 no. 5 - August 2014. 48 Wear of different material pairings for the cylinder liner - piston ring contact. Thomas Wopelka, et al. Industrial Lubrication and Tribology. DOI 10.1108/ILT-07-2017-0218. 49 On the Mechanism of ZDDP Antiwear Film Formation. Zhang, Jie; Spikes, Hugh. Imperial College London, London, UK. DOI: 10.1007/s11249-016-0706-7 50 The influence of start-stop transient velocity on the friction and wear behavior of a hyper-eutectic Al-Si automotive alloy. J.C. Walker, et al. National Centre for Advanced Tribology at Southampton. 51 Sliding wear behavior of eutectic Al-Si alloy under lubricated conditions: An investigation on the effect of ethanol (E85) addition. Victor Vimalrajan Francis. University of Windsor. LN Engineering Technical Library. Copyright ©2019 LN Engineering LLC