National Oil & Lube News

March 2017

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66 NOLN | www.noln.net VIEWPOINT Selling is Educating Unintended Consequences Drive GDI Engines to Shops: Knock, for Customers & Service Writers by Amber Kossak with Owen Heatwole Here's an exchange between a customer and a service writer: Customer, "My fairly new vehicle seems to have lost power and fuel mileage. Can you help?" Service writer, "Our check indicates that your knock sensor(s) caused changes to save your engine from damage." Customer, "But I haven't heard knock- ing! What's going on here?" Both are likely correct. Read on. For the Service Writer — Knock Evidence Knock can destroy turbocharged gasoline direct injection (TGDI) engines — a dom- inant design including all Ford EcoBoost engines. Research showed that, "[With TGDI] downsizing and increasing power output, the failure mechanisms started to become more clear … e rods tend to fail first, and the second ringland follows … peo- ple that lose their motors on the highway … speak about a cloud of black smoke … caused by a LSPI [low speed pre-ignition or super-knock] event." Digitaltrends.com/cars explained the knock difference between gasoline and diesel engines, "In a gas engine, the air and fuel is compressed and at a critical point in the timing of the cycle, a spark plug ig- nites the gas. "But in a diesel engine, there are no spark plugs. When diesel fuel and air are squeezed enough, the extreme compres- sion generates enough heat that the mix- ture essentially spontaneously combusts. is is known as 'compression ignition,' and it's the basis of how a diesel engine works. "When a gasoline engine has combus- tion ignition, we often call it 'knock,' and it can ruin the engine. "But diesel engines are built to take ad- vantage of it." In GDI engines, more gasoline com- bined with higher compression produces unburned fuel droplets that cause in- creased combustion chamber hot-spot de- posits. ese increase knock — as verified by more than 2,000 Society of Automotive Engineers technical papers and journal ar- ticles that contain all the words "gasoline direct injection knock." Super-Knock Can Catastrophically Destroy Engines If knock can damage an engine, then su- per-knock, or LSPI, can cause a catastro- phe. A new 2017 SAE Paper No. 2017-01- 0686, named "Effect of Timing and Lo- cation of Hotspot on Super Knock during Pre-ignition," reported, "Pre-ignition in SI [spark ignition] engine is a critical issue that needs addressing as pre-ignition may lead to engine knocking events that may damage engine catastrophically. … ema- nates from hot-spots inside the combus- tion chamber." Numerous sources provide additional information on this subject. "Downsizing is an important concept to reduce fuel consumption as well as emissions of spark ignition engines. … engines are boosted … at high loads and low engine speed referred to as low-speed pre-ignition or LSPI. … the air/fuel mix- ture is ignited prior to the spark which results in the initial flame propagation quickly transforming into heavy engine knock. Very high pressure rise rates and peak cylinder pressures could exceed de- sign pressure limits, which in turn could lead to degradation of the engine," accord- ing to SAE Paper No. 2011-01-0342, "En- gine Operating Condition and Gasoline Fuel Composition Effects on Low-Speed Pre-Ignition in High-Performance Spark Ignited Gasoline Engines." University of Wisconsin research re- ported, "Super-knock can suddenly dam- age the engine due to the extremely high peak pressure ... triggered by 'hot-spot' other than spark prior to the spark timing. … com- mon knock suppres- sion methods, including retard sparking timing … are not effective for super-knock." For the Customer — Who Doesn't Hear Knock Believe it or not, your customers won't al- ways hear their engines knocking. According to SAE Paper No. 2014-01- 1212, "Investigation on Pre-ignition and Super-Knock," motorists may remain un- aware of knock due to noise-reducing ve- hicle designs. Super-Knock and the Solution LSPI super-knock causes problems includ- ing broken pistons and bent connecting rods, with traffic safety hazards report- edly causing OEM abandonment of early designs. Service shops may still encounter vehicles with older designs that have been eliminated or updated by the manufac- turer, and motorists may be unaware of knock damage. e solution is to offer your customers preventive maintenance control of com- bustion chamber deposits that cause hot- spots and LSPI super-knock. S Author's note: Information sources and photos available upon customer request. AMBER KOSSAK is president and CEO of Solid Start, man- ufacturer of True Brand Products. She has been in the automotive industry for almost 20 years and is serving on the AOCA board of directors. She can be contacted at: kossak@solidstart.biz For more information please visit: www.solidstart.biz OWEN HEATWOLE serves as Technical Support manager of Solid Start/True Brand. He's spent his life maintaining a variety of engines and the last 25 years supporting pre- ventive maintenance engine decarbonization, including projects for the AMRA's Technical Committee and training worldwide. He can be contacted at: heatwole@solidstart.biz

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