The efficient choice among combustion engines

The efficient choice among combustion engines
ETH researchers redesigned the conventional diesel engine of a VW Golf to run on 90% natural gas. Credit: Tobias Ott / ETH Zurich

( —Researchers at ETH Zurich have developed an internal combustion engine that emits less than half the CO2 compared to a regular engine without compromising performance. This corresponds to fuel consumption of less than 2.4 l per 100 km. This natural gas-diesel hybrid engine is based on a system of sophisticated control engineering.

The global energy markets are changing. New extraction methods are tapping into oilfields and natural gas deposits that have been inaccessible until now. The US, for example, is able to cover up to 83% of its total energy needs today; the government is even planning to increase exports of natural gas in the future. And there are new developments on the horizon: natural gas may also become an important fuel for vehicles on America's roads, thanks to the work of Swiss researchers at the Institute for Dynamic Systems and Control at ETH Zurich. They have developed a natural gas-diesel hybrid powertrain that emits just half the CO2 without compromising performance.

Diesel fuel injection instead of an ignition plug

ETH researchers redesigned the conventional diesel of a VW Golf to run on 90% natural gas. Instead of a spark plug as is standard with natural gas engines, the engine is ignited with a small amount of diesel injected directly into the cylinder. In doing so, the researchers were able to achieve a highly efficient combustion with a of 39.6%.

Natural gas- already exist, and are used industrially where power is generated and used in one place – for example to operate large machinery. "In a vehicle, the engine speed and load change constantly, which means the engine system is far more complicated," explains Tobias Ott, a doctoral student in Professor Lino Guzzella's research group.

Video about ultra-efficient hybrid engine.

Innovative electronic combustion control

Ott developed the innovative electronic combustion control together with senior scientist Christopher Onder as part of his dissertation. A sensor that measures pressure in the cylinders plays a key part: using complex control algorithms, the researchers were able to adapt the amount and timing of diesel continually, allowing an engine system with highest efficiency. The researchers also linked the innovative natural gas-diesel engine to a small electric motor to further reduce consumption. However, it could also be installed in a vehicle without electric hybridisation, which would be crucial for industrial production in larger quantities.

Mass production – a possibility in five years' time

The researchers demonstrated the reduction in emissions with experiments on a specially designed test rig and recently published the results in the specialist journal Energies. This proof of concept also involves solving final technical problems. "At the moment, we are concentrating particularly on the temperature in the catalytic converter," says Ott. For the converter to get up and running, it has to reach at least 300 degrees. "Our combustion engine converts heat energy into mechanical energy with such efficiency that the exhaust gas is not warm enough to create sufficient heat, particularly after start-up," adds Ott. The researchers want to solve the problem by modified control of the engine during the warm-up.

Christopher Onder is convinced that the -diesel engine can be produced in series production in five years. "The prerequisite is that we find an industrial partner who can take charge of developing a prototype," he explains. The researchers believe that the success of their engine depends critically on its production costs. They stress that their solution may not be cheap, but it is comparatively cost-effective. And because their concept is based on technology that already exists, it can be implemented quickly and is the perfect bridging technology for the next 10 to 20 years. The researchers are already engaged in negotiations with a car manufacturer.

Explore further

Delphi gasoline-injection engine technique rivals hybrid's edge

More information: Ott, T., Onder, C. and Guzzella, L. Hybrid-Electric Vehicle with Natural Gas-Diesel Engine, Energies, 2013. 6: 3571-3592. DOI: 10.3390/en6073571
Provided by ETH Zurich
Citation: The efficient choice among combustion engines (2013, September 12) retrieved 21 July 2019 from
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Sep 12, 2013
awesome work!

Sep 12, 2013
That's nice. It's a dead end, though. Effort would be better spent finding something with an efficiency far higher than 39.6%.

Sep 12, 2013
If we need to use fossil fuels, then I want this under the hood:

Sep 12, 2013
In Perth, Western Australia we have converted many diesel buses to CNG, which is mostly methane but, I am not sure if they use any of this technology, this was a few years after a Hydrogen bus trial which did nothing except prove Hydrogen is useless as a terrestrial fuel source and BP got lots of money... Anyway here is a reference link of sorts, I will be looking into the "Transperth Gasbus" some time later this year in preparation for another project,


Sep 12, 2013
PPihkala offered one of his immutable goals
If we need to use fossil fuels, then I want this under the hood:

Saw this about 4 years ago, the question arises, where is it now ?
The issue of power vs size is a bit misleading, I know of a V8 not far from me that produces 1100 hp easily but can it do it for long, so the comparison on the link provided might not be qualified for sustained output - such as is needed for the engines of prime movers that, in Australia, can have 4 trailers and carry lottsa tonnes several hundred Kms day day out all around the year...

Sep 12, 2013
Effort would be better spent finding something with an efficiency far higher than 39.6%.

Oscillating engines in which the piston rises and falls come up against the problem of having to evacuate a chamber full of hot gas vastly out of equilibrium, in order to make room for the next intake / compression strokes. All positive displacement engines seem to incorporate this same intrinsic design flaw, and it's the main reason for their limited efficiency - indeed, 40% is around the theoretical limit.

The solution is a positive displacement turbine - in which the piston travels through a toroidal cylinder, in one direction. It only needs 3 strokes, each simultaneous and constant, in 3 discrete rings, which can be nested or stacked, with interconnecting ports. The first stage, compression, can be achieved via dynamic impeller (ie. 'periflow') types, as only combustion and expansion require positive displacement.. This could rinse far more work from the hot gas prior to release

Sep 13, 2013
MrV, very interesting that positive displacement turbine. I've heard of several very efficient prototypes like that. However, it seemed that subjecting such engine/turbines to g forces caused the moving pistons to quickly make contact with the curved walls and get stuck. Reminds me of throwing a stone down a deep well: After a while it will start bouncing back and forth between the walls, which for the prototypes meant catastrophic failure. Have you heard of any improvements?

Sep 13, 2013
I have not... unfortunately. There was a German group going under the name "ring motor", which used disc valves - radially-oriented rotating discs, with a hole the same diameter as the piston, intercepting the toroid cross-section at four quadrants to form transient chambers. These valves were synced to allow the piston to pass through, just before it slammed into them. I don't know what happened to the company, they went offline years ago. I suspect that the valve timing was too critical for practical implementations though - if for any reason the hole in the disc didn't align perfectly to the approaching piston, the collision would be catastrophic...

And i should fess up that my idea above has its own Achilles heel, in that it requires a main engine gasket that is also the main bearing for the two contra-rotating halves... diametrically conflicting requirements i was never able to reconcile, alas..

Doubtless many similar ideas have hit the same bearing/gasket problem... :(

Sep 15, 2013
I wonder if consumers will appreciate how much more complicated and time consuming filling up at the gas station will be.

Sep 15, 2013
"The US, for example, is able to cover up to 83% of its total energy needs today; the government is even planning to increase exports of natural gas in the future"

Fracking is only affordable above $80/barrel. USA is exporting gas because it is a short-term economy with everything and everyone for sale. Dick Cheney specifically rammed a bill through congress which declared fracking chemicals to be a trade secret exempt from the EPA. Once environmental costs of injecting carcinogenic chemicals into aquifers and installing water purification plants in every water well are included, the real cost of fracking is in the hundreds of dollars per barrel. Of course feral capitalist Americans prefer drinking toxic sludge and allowing petrol monopolies to externalize the costs onto the Obamacare medical system. Millions of dying Americans will be hooked up to life support and undergo chemotherapy. A new healthcare industry will boom!

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