Radical Engine Redesign Reduces Pollution, Oil Consumption

[The Grim Squeaker]

Radical Engine Redesign Would Reduce Pollution, Oil Consumption

Science Daily — Researchers have created the first computational model to track engine performance from one combustion cycle to the next for a new type of engine that could dramatically reduce oil consumption and the emission of global-warming pollutants.

Gregory M. Shaver, from left, an assistant professor of mechanical engineering at Purdue, and graduate student David Snyder discuss how to modify a commercial diesel engine with a new technology that promises to dramatically reduce oil consumption and the emission of global-warming pollutants. Graduate student Gayatri Adi (background) reviews software algorithms needed for the new technology, called homogeneous charge compression ignition. (Credit: Purdue News Service photo/David Umberger)

"We're talking about a major leap in engine technology that could be used in hybrid cars to make vehicles much more environmentally friendly and fuel stingy," said Gregory M. Shaver, an assistant professor of mechanical engineering at Purdue University.

A key portion of his research, based at Purdue's Ray W. Herrick Laboratories, hinges on designing engines so that their intake and exhaust valves are no longer driven by mechanisms connected to the pistons. The innovation would be a departure from the way automotive engines have worked since they were commercialized more than a century ago.

In today's internal combustion engines, the pistons turn a crankshaft, which is linked to a camshaft that opens and closes the valves, directing the flow of air and exhaust into and out of the cylinders. The new method would eliminate the mechanism linking the crankshaft to the camshaft, providing an independent control system for the valves.

Because the valves' timing would no longer be restricted by the pistons' movement, they could be more finely tuned to allow more efficient combustion of diesel, gasoline and alternative fuels, such as ethanol and biodiesel, Shaver said.

The concept, known as variable valve actuation, would enable significant improvements in conventional gasoline and diesel engines used in cars and trucks and for applications such as generators, he said. The technique also enables the introduction of an advanced method called homogeneous charge compression ignition, or HCCI, which would allow the United States to drastically reduce its dependence on foreign oil and the production of harmful exhaust emissions.

The homogeneous charge compression ignition technique would make it possible to improve the efficiency of gasoline engines by 15 percent to 20 percent, making them as efficient as diesel engines while nearly eliminating smog-generating nitrogen oxides, Shaver said.

This improved combustion efficiency also would reduce emission of two other harmful gases contained in exhaust: global-warming carbon dioxide and unburned hydrocarbons. The method allows for the more precise control of the fuel-air mixture and combustion inside each cylinder, eliminating "fuel rich" pockets seen in conventional diesel engines, resulting in little or no emission of pollutants called particulates, a common environmental drawback of diesels.

The variable valve actuation system makes it possible to "reinduct," or reroute a portion of the exhaust back into the cylinders to improve combustion efficiency and reduce emissions. The system also makes it possible to alter the amount of compression in the cylinders of both conventional and HCCI engines and to adjust the mixing and combustion timing, allowing for more efficient combustion.

"Variable valve actuation and HCCI would help to significantly reduce our dependence on oil by enabling engines to work better with ethanol and biodiesel and other alternative fuels," Shaver said. "But accomplishing this is going to require a strong effort in several research areas - a commitment of funding, people power, industrial involvement and academic involvement."

In HCCI, the "charge," or fuel-air mixture, is homogeneous, meaning it is uniform. Adding the reinducted exhaust both dilutes and increases the temperature of this air-fuel mixture before compression. The process also allows for a uniform "auto ignition," or combustion without the need of a spark, at a lower compression than normally required for diesel engines, reducing engine wear and tear.

Inside the cylinders of ordinary internal combustion engines, there is a large temperature difference, or gradient, between portions of the air-fuel mixture that have been ignited and portions that are still not burned. The homogeneous fuel-air mixture and reinducted exhaust work together to eliminate this temperature gradient during the auto-ignition, which decreases the overall combustion temperature. Decreasing the combustion temperature is a key step in dramatically reducing nitrogen oxides.

A major challenge will be learning how to automatically adjust valve motions and fuel injection to match changes in operating conditions dictated by factors such as a vehicle's varying speed, how much weight it is carrying and what type of fuel is being used.

Engines incorporating HCCI will use sensors to monitor an engine's performance, providing crucial data needed to dynamically alter the valves' timing. Controlling the combustion process via variable valve actuation will require specialized software algorithms being developed by the Purdue researchers.

"We will use feedback control, where you have sensors that provide data from the engine and an algorithm to precisely control the valves," Shaver said.

Shaver, his colleagues and students are in the process of building a one-of-a-kind multicylinder engine design with "fully-flexible variable valve actuation," which will allow the study of HCCI and alternative fuel combustion, he said.

He was the lead author of a research paper honored with the 2006 Rudolf Kalman Paper Award for the best paper published in the Journal of Dynamic Systems, Measurement, and Control. The award was issued last year during the International Mechanical Engineering Conference and Exposition in Chicago. The paper detailed findings related to a new mathematical model to help develop the homogeneous charge compression ignition system.

In order for the system to work, it is critical to track changing engine performance from one combustion cycle to the next. The mathematical model Shaver has developed is the first of its kind to precisely track this dynamic cycle-to-cycle performance and other data.

The highest efficiency would be realized by combining HCCI technologies in hybrid vehicles that use an electric motor in addition to an internal combustion engine. "It's essential to continue research on multiple fronts, including work to tackle problems associated with fuel cells and hybrid systems and understanding how to incorporate the advanced combustion engines on hybrid powertrains," he said.

U.S. petroleum imports are predicted to increase about 35 percent by 2030. At the same time, the transportation-related emission of carbon dioxide is expected to rise by about 35 percent in the United States.

The authors of the paper published last year in the Journal of Dynamic Systems, Measurement, and Control were Shaver; J. Christian Gerdes, an associate professor of mechanical engineering at Stanford University; Matthew J. Roelle, a graduate student at Stanford; Patrick A. Caton, an assistant professor at the U.S. Naval Academy; and Christopher F. Edwards, an associate professor of mechanical engineering at Stanford.

Shaver's research team at Purdue includes graduate students David Snyder, Gayatri Adi and Anup Kulkarni, undergraduate students Armando Indrajuana, Elena Washington, Justin Ervin and Matt Carroll.

Further Information

Article: Dynamic Modeling of Residual-Affected Homogeneous Charge Compression Ignition Engines with Variable Valve Actuation

Gregory M. Shaver, J. Christian Gerdes, Matthew J. Roelle, Patrick A. Caton, Christopher F. Edwards Department of Mechanical Engineering, Stanford University

Abstract: One practical method for achieving homogeneous charge compression ignition (HCCI) in internal combustion engines is to modulate the valves to trap or reinduct exhaust gases, increasing the energy of the charge, and enabling autoignition. Controlling combustion phasing with valve modulation can be challenging, however, since any controller must operate through the chemical kinetics of HCCI and account for the cycle-to-cycle dynamics arising from the retained exhaust gas. This paper presents a simple model of the overall HCCI process that captures these fundamental aspects. The model uses an integrated Arrhenius rate expression to capture the importance of species concentrations and temperature on the ignition process and predict the start of combustion. The cycle-to cycle dynamics, in turn, develop through mass exchange between a control volume representing the cylinder and a control mass modeling the exhaust manifold. Despite its simplicity, the model predicts combustion phasing, pressure evolution and work output for propane combustion experiments at levels of fidelity comparable to more complex representations. Transient responses to valve timing changes are also captured and, with minor modification, the model can, in principle, be extended to handle a variety of fuels.

Interesting.. Not nearly enough of course but should be useful for the few who'll still have a use for a car in two decades or so.

[Napoleon the Clown]

This sounds a lot like a much more complex version of the already existant variable valve timing. Adding this level of complexity to an already highly complex system doesn't sound like the most brilliant solution to me. The biggest question is, is the increased complexity going to produce results worth the extra production costs and the increased risk of breaking down?

While 15%-20% increase is nice and all, more can be done with simpler solutions. Minimizing weight while keeping a vehicle safe being one such solution. Variable valve timing as it currently exists (such as the Honda Civic V-TEC) helps. Keeping the low-RPM torque at a modest level will keep engine revs lower and help out there... There's a lot of things we can do now that'll be more reliable.

Long term we really need to go for something other than carbon-based fuels. But that's stating the obvious.

[Sea Skimmer]

The auto industry is chock full of hopelessly complicated schemes to improve gasoline fuel economy. The Saab variable compression ratio engine comes to mind, god help you if your cylinder head overheats even slightly. I really like one Mercedes Benz concept now being tested, in which the exhaust is used to heat water for an auxiliary steam turbine, proving a claimed 15% improvement in efficiency. My favorite part is that following the best traditions of Nazi Uberwaffen, it uses not one but two separate steam cycles to do it.

I’m sure that if enough of the technology now being thrown was combined, we could build a gas engine with better fuel economy then a non turbo diesel, and it would only cost ten times as much with five times the moving parts and maybe two-three times the weight.

[Starglider]

This sounds a lot like a much more complex version of the already existant variable valve timing. Adding this level of complexity to an already highly complex system doesn't sound like the most brilliant solution to me.

From the OP;

The new method would eliminate the mechanism linking the crankshaft to the camshaft, providing an independent control system for the valves.

These systems work by replacing the cams (and associated cam shaft and drive chain/belt) with solenoids. Solenoids are extremely reliable and mechanically simple. This system will experience less mechanical friction and wear before you even consider the combustion efficiency benefits. The additional complexity is electronics and software, and additional solid state complexity is generally preferable to mechanical moving parts complexity.

The biggest question is, is the increased complexity going to produce results worth the extra production costs and the increased risk of breaking down?

There is no additional risk of breaking down. In fact there is an advantage in that the failure of one valve actuator will not affect the other valves and you can drive to a garage on the remaining cylinders. A failure in current cam mechanisms, though rare, will generally disable the engine.

There is a minor increased production cost, but most of the expense would be R&D.

Minimizing weight while keeping a vehicle safe being one such solution.

Minimizing vehicle weight is tough given current safety standards and the consumer preference for lots of ancillary equipment.

Long term we really need to go for something other than carbon-based fuels. But that's stating the obvious.

The corresponding Slashdot article is somewhat amusing; it has quite a few posters going 'no, no, we just need to switch to biofuels, they're carbon neutral, everything will be fine and I can keep my pickup truck'.

[Napoleon the Clown]

This sounds a lot like a much more complex version of the already existant variable valve timing. Adding this level of complexity to an already highly complex system doesn't sound like the most brilliant solution to me.

From the OP;

The new method would eliminate the mechanism linking the crankshaft to the camshaft, providing an independent control system for the valves.

These systems work by replacing the cams (and associated cam shaft and drive chain/belt) with solenoids. Solenoids are extremely reliable and mechanically simple. This system will experience less mechanical friction and wear before you even consider the combustion efficiency benefits. The additional complexity is electronics and software, and additional solid state complexity is generally preferable to mechanical moving parts complexity.

Ah, I see.

The biggest question is, is the increased complexity going to produce results worth the extra production costs and the increased risk of breaking down?

There is no additional risk of breaking down. In fact there is an advantage in that the failure of one valve actuator will not affect the other valves and you can drive to a garage on the remaining cylinders. A failure in current cam mechanisms, though rare, will generally disable the engine.

There is a minor increased production cost, but most of the expense would be R&D.

Good point.

Minimizing weight while keeping a vehicle safe being one such solution.

Minimizing vehicle weight is tough given current safety standards and the consumer preference for lots of ancillary equipment.

Which is why I added "keeping a vehicle safe". To be fair, you can meet safety standards and still have a light-weight vehicle. Take any number of performance cars. The notoriously light-weight Lotus models are a good example. Intelligent engineering will help make both possible.

Long term we really need to go for something other than carbon-based fuels. But that's stating the obvious.

The corresponding Slashdot article is somewhat amusing; it has quite a few posters going 'no, no, we just need to switch to biofuels, they're carbon neutral, everything will be fine and I can keep my pickup truck'.

Ah, optimists... Any alternatives (non-carbon means biofuels are out) are a long term solution. I'm in favor of improving what we have until a realistic solution is found/developed.

[Sea Skimmer]

This sounds a lot like a much more complex version of the already existant variable valve timing.

Yup. A system already exists which uses a hydraulic cylinder to move the camshaft to constantly vary valve timing, better then V-tec. If the system breaks, the engine will still run at its default settings. Systems also exist to directly vary valve lift height, removing the need for a throttle plate and thus eliminating pumping losses. This will significantly improve fuel economy during low rpm city driving and even when idling.

As for the reliability of solenoids, it is very good, but then they also break on starter motors all the time. Making one that can actuate thousands of times per minute for 150,000 miles of driving under varying temperature and vibration conditions will be an impressive feat. The only way to prove the technology will be to actually drive a car with the system for that kind of distance. We shall wait and see, I think my automative text book has at least ten different major engine redesign concepts in it all promising better fuel economy for gas engines.

[aerius]

These systems work by replacing the cams (and associated cam shaft and drive chain/belt) with solenoids. Solenoids are extremely reliable and mechanically simple. This system will experience less mechanical friction and wear before you even consider the combustion efficiency benefits. The additional complexity is electronics and software, and additional solid state complexity is generally preferable to mechanical moving parts complexity.

They tried this with gasoline engines already, at high RPM the solenoids ended up consuming almost as much power as the engine produced, and in early prototypes the valvetrain actually used more power than the engine put out.

The good old camshaft is surprisingly efficient and reliable, especially now that we have roller lifters and so forth which greatly reduce friction.