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Tsinghua team uses optical diagnostics to analyze source of sporadic super-knock in advanced SI engines

Knock is one of several different well-known abnormal combustion processes in spark-ignition engines; most of these abnormal combustion issues have been addressed with improved design or control schemes as well as fuel specifications. However, emerging advanced SI engines—e.g., those with turbocharging and direct injection—can exhibit a new phenomenon: super-knock, or violent engine knock.

Super-knock can damage engine components within only a few cycles. Because the events are sporadic and uncontrolled, it has been difficult to assess the causes and devise solutions.

In a new paper in the journal Fuel, a team from Tsinghua University has used optical diagnostics to analyze the progression from pre-ignition to super-knock. This work is a follow-on to the team’s earlier study distinguishing between pre-ignition and super-knock. (Earlier post.)

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By utilizing a rapid compression machine, events of pre-ignition and super-knock in a closed system under high temperature and high pressure were captured by synchronous high-speed direct photography and pressure measurement, with the results demonstrating that the mechanism of super-knock is constituted by hotspot-induced deflagration to detonation followed by high-pressure oscillation (DDP).

—Wang et al.

Resources

  • Zhi Wang, Yunliang Qi, Xin He, Jianxin Wang, Shijing Shuai, Chung K. Law (2015) “Analysis of pre-ignition to super-knock: Hotspot-induced deflagration to detonation,” Fuel, Volume 144, Pages 222-227 doi: 10.1016/j.fuel.2014.12.061

Comments

gorr

I knew that all the latest innovations for ice engines were not a panacea and on the contrary were a step down instead. im not interested in direct injection and higher compression and also by stop start and low rolling resistance tires and also I hate abs breaks. All that is costly, high possible risks and more troubles overall. Since they implemented electronic fuel injection and ignition they never discover or implemented nothing better and now that gas prices are getting lower, than it's more obvious. My next car purchase will probably be a used Nissan micra, cheap and simple and high mpg. I don't need a leaf or volt or prius or skyactiv mazda or ecoboost ford. These are troublesome costly subpar technology and harassing marketing gimmick enforced by laws and fraudulent subsidies. Also they sell suppar gasoline now containing rust prone 10% ethanol for a net 3% decrease in btu content, all that at the expence of car owners and it hurt badly small motorcycles engines and lawnmower having carburators. All we see here is marketing gimmicks.

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