Turbocharging the switch to efficient engines

Turbocharging the switch to efficient engines
A fuel injector can be heavily damaged by a pre-ignition event (bottom); a new injector is shown above. Credit: Eshan Singh

Predicting capricious pre-ignition combustion events could enable automakers to build powerful yet more efficient engines.

A combustion problem that has troubled manufacturers since the industry began still plagues the designers of fuel-. A team at KAUST's Clean Combustion Research Center, led by Robert Dibble, focuses on understanding pre-ignition.

A single occurrence of pre-ignition—when fuel ignites prematurely in the engine cylinder to release a mistimed kick of energy—can cause major damage. Pre-ignition is sporadic and unpredictable. It is more prevalent in the downsized, turbocharged engines that are now producing for improved while maintaining power output.

"Pre-ignition remains a bottleneck to further downsizing and improving engine efficiency," explains Eshan Singh, a Ph.D. student in Dibble's team.

The team systematically changed engine parameters, including air intake temperature and exhaust back-pressure, thereby establishing the conditions most likely for pre-ignition. For example, the team observed more pre-ignition events with a higher exhaust back pressure: this occurs when the engine cylinder has less effective emptying of burnt fuel between combustion cycles.

Turbocharging the switch to efficient engines
Ph.D. student Eshan Singh working on the KAUST pre-ignition engine. Credit: Raheena Abdurehim

The researchers combined all their observations to build a picture of the pre-ignition phenomenon. "Our work unravels the pre-ignition event is divided into several steps," Singh says.

A pre-ignition event originates during the previous fuel combustion cycle, when fuel injected into the cylinder interacts with oil on the cylinder liner forming an oil-fuel droplet. At the end of each combustion cycle, the oil-fuel droplet is usually expelled from the cylinder; however, from time to time, the oil-fuel droplet remains and may trigger pre-ignition in the following cycle, the team showed. "Car makers need to break this chain of events to suppress pre-ignition," Singh says.

Stopping the fuel and oil from interacting, or completely exhausting all the burnt mixture from the engine, are two points where the event chain can be broken. Preventing the injected from hitting the oil-coated liner is one approach. "We are looking at practical methods to reduce pre-ignition by changing the injection strategy," Singh says. "We have filed a patent that uses injection strategies to provide pre-ignition-free operation without compromising engine power."

Other routes to break the chain of events demand deeper understanding of pre-ignition, Singh adds. "Our exciting discoveries are gratifying. Going forward, we are motivated to uncover additional controlling variables that allow for more accurate pre-ignition predictions."

Due to graduate from KAUST in the fall of 2019, Eshan is currently interning at the Combustion Research Facility in Sandia National Laboratories, California. There, he is exploring mixed-mode combustion for future internal combustion engines. "This experience has already exposed me to a plethora of tools that are frequently used in engine diagnostics. Several new avenues have now opened for my research career, which is vested in tackling solutions to combat ."


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More information: Mechanism Triggering Pre-Ignition in a Turbo-Charged Engine. DOI: 10.4271/2019-01-0255
Citation: Turbocharging the switch to efficient engines (2019, March 28) retrieved 18 August 2019 from https://phys.org/news/2019-03-turbocharging-efficient.html
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Mar 28, 2019
Searching for ways to improve the fuel efficiency of the engine is a game of diminishing returns, because the temperature and pressure of the engine cannot be increased without it producing NOx. You can't increase the thermal efficiency by many percentage points anymore, and the remaining means to tease another fraction of a percent more is leading to more expensive and less robust engines that still pollute in ways that aren't (yet) being tested.

The whole topic is a red herring, and only a matter of consideration because governments keep pushing impossibly high fuel economy standards that are forcing bad compromises and reward the cheaters like Volkswagen.

They should be looking into ways to make more fuel in environmentally friendly ways. Synthetic fuels that store renewable energy. How much fuel your car uses then would be only an issue for your wallet - and nobody else's business.

Mar 28, 2019
Eikka, for a person who argued with me at great length about electric vehicles (EVs), your comment stops just short of concluding EVs are the solution to your diminishing returns problem. My advice is to sidestep a whole host of problems with trying to further improve the internal combustion engine (ICE) and purchase a Tesla or other EV instead.

https://www.tesla.com/

Mar 28, 2019
In the wanning days of the steam locomotive, there were most likely building full of people that were experts with steam trying to get the efficiency up from around 5%(just a guess) and then BAM...the diesel came and all that steam expertise went out the window.

The IC engine is on it's last legs. I wouldn't waste a career on IC engines at this stage.

Mar 29, 2019
On a related note, Union Pacific has been restoring a 4-8-8-4 "Big Boy" steam locomotive these last few years at their Cheyenne, Wyoming works. UP 4014 is now reportedly back together after a massive overhaul. (It had been sitting outside at a California museum for decades.) It is expected to be in Ogden Utah on May 10, 2019 for the sesquicentennial celebration of the of the first transcontinental railroad, then join UP's excursion fleet. Man, it is going to be impressive as all get out to see one of these behemoths in action again.

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