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Stratified Charge Engine With Two-Stage Combustion Mechanism Shows 17% Reduction in Fuel Consumption Without Direct Injection

Two-stage combustion mechanism in twin swirl combustion (1, zone containing pure air; 2, spark plug; 3, turbulizer; and 4, zone containing the fuel-rich mixture). Click to enlarge. Credit: ACS

A team of researchers from Istanbul Technical University (ITU) in Turkey has presented a 1.6-liter stratified charge gasoline engine featuring a twin swirl combustion chamber operating with a two-stage combustion mechanism and experimentally shown that it can deliver a 17% reduction in fuel consumption with a 7% increase in power compared to a conventional 1.6-liter port-injected engine.

The proposed combustion mechanism does not require high fuel injection pressures and can be applied on current production engines without significant modification and without direct injection fuel systems, according to the researchers. A paper on the work was published online in the ACS journal Energy & Fuels on 15 December.

The two-stage combustion mechanism was originally proposed by a team comprising researchers from Azerbaijan Technical University (AzTU), Warsaw Technical University (WTU), ITU, and Middle East Technical University (METU).

In conventional gasoline engines, every part of the cylinder contains a mixture having an excess air ratio (λ) of approximately 1. Stratified charge engines have frequently stoichiometric mixture (λ = 1) only near the spark plug and lean mixture in the cylinder, globally. For the special case of stratified charge engines operating with a two-stage combustion mechanism, there is a lean mixture in the cylinder globally as well; however, there is a fuel-rich mixture in the vicinity of the spark plug.

The nonhomogenous mixture in stratified charge engines is obtained usually with the modification of the piston geometry. The geometry of the intake manifold can also be modified. Because there is a lean mixture in the combustion chamber globally, stratified charge engines have a lower knock tendency than the conventional gasoline engines. Because of this fact, the compression ratio (ε) of a stratified charge engine can be higher than the compression ratio of a conventional gasoline engine; ε ≥ 12 is possible. A higher compression ratio leads to a higher efficiency. The absence of throttle losses in part load operation in combination with the ability to use higher compression ratios leads to lower fuel consumption.

—Dinc et al. 2008

The proposed combustion chamber looks like a figure “8” and is separated into two zones. The spark plug mounted part of the combustion chamber contains a fuel-rich mixture with an excess air ratio of 0.6-0.8, while the other part contains pure air. The fuel is injected into the intake manifold and fed into the zone containing the fuel-rich mixture. The intake manifold is designed for the two-stage combustion mechanism, such that it increases the swirl effect and volumetric efficiency. The counter-rotating swirling motion—which occurs during the intake and compression cycles of the engine—does not allow the mixing of the two zones until ignition time. This allows stratification of the air-fuel mixture across the load range.

Because the swirl motion occurs with the start of the intake cycle, the air-fuel mixture can be prepared in the intake manifold (outside of cylinders). Therefore, current electronic injection systems or carburetor engines can be used with this method. In other words, special and expensive direct-injection systems are not required, such as in gasoline direct injection (GDI) engines, where the injection of fuel into the cylinder reduces the time available for evaporation and mixing.

—Dinc et al. 2008

The two-stage combustion mechanism can also reduce emissions of criteria pollutants. Because the liquid phase of the gasoline does not contact the cold wall of the cylinders, and because the counter-rotating swirling motion reduces the contact of the flame with the piston, the stratified charge engines with the twin swirl combustion chamber produce lower hydrocarbon (HC) emissions. Incomplete combustion products (CO and H2 produced during the combustion of the rich mixture (λ = 0.6-0.8) at the first stage can be burned in the second stage of combustion with the effect of the swirl motion. The lack of oxygen in the rich mixture and low combustion temperature at the first stage of combustion do not allow NOx formation.


  • Cenk Dinc, Hikmet Arslan and Rafig Mehdiyev (2008) CO2 Emission Reduction Using Stratified Charge in Spark-Ignition Engines. Energy Fuels, Article ASAP doi: 10.1021/ef800349x



Good new for ICE extended life.

What has the Big-3 been doing for the last 50+ years with their steady 20 mpg vehicles.

It seems that a mid-size ICE vehicle could do 50+ mpg if all known technologies were fully and properly integrated.

Brian P

Let's see independent test results that confirm compliance with Euro 5 and/or US EPA Tier 2 bin 5 before making the "good news ... what has the Big 3 been doing" type comments.

This seems conceptually like Honda's CVCC system they used in the 1970's, albeit the method of creating the stratification is different. Honda doesn't use CVCC any more. They HAVE used lean-burn (without direct injection) since then - example, the Honda Insight engine - but not in engines that meet Euro 5 or Tier 2.

Reason: Three-way catalysts can't reduce NOx when they are fed an exhaust stream that is overall lean, and stratified-charge concepts don't reduce NOx sufficiently for the engine-out emissions to meet current standards. In between the "rich" and "lean" zones there is unavoidably a "near stoichiometric" zone that produces too much NOx for the engine-out emissions to meet current standards.

If you can figure out a way to fire a mixture that is lean throughout (or diluted with enormous EGR) then maybe engine-out NOx can be reduced ... but that's called HCCI, and not stratified charge, and HCCI is extremely challenging to make it work properly.

Or, you can use the same de-NOx catalysts that current diesel engines use. But if you are going to do that ... you might as well go with a diesel engine because it will be more efficient than spark-ignition stratified charge ...


Nothing new here. I even drove a Honda Civic CVCC back in the 1970s. I must say it was a piece of sh_t. It was bought new, blew a head gasket at 50,000 miles.


Props for creativity, though I'd be curious to see how this design affects pumping losses.


With Tank to Wheel efficiency, currently between 15% and 20%, there is lot of room for future improvmemts.

How much has it really been improved over to last 30 years?...60 years?...90 years?

Couldn't all the affordable new techniques be applied to double the current ICE vehicles overall efficiency?

A 40+ mpg mid-size affordable ICE vehicle should be possible to build without too many compromises.

A 60+ mpg affordable mid-size HEV is also a short term possibility.

Bailouts carrots may help to convince manufacturers to do more.

Brian P

There is room for "fuel consumption" improvement. But within the constraints imposed by emission standards, there is not room for all of that much improvement to come from the ICE itself.

The only way to (come close to) double the efficiency of a spark ignition engine is to substitute a diesel engine. Diesel engines on an automotive scale are already at approx 42% peak efficiency at the point of best BSFC and they have been in this range for the last 10 - 15 years. The emissions have been drastically improved in that time, but the lack of improvement in best BSFC suggests we've gotten close to all there is to get - unless someone decides that NOx emissions are not as important as some people think they are, and even then, the loss in efficiency due to the NOx emission controls is only a few percent. (I do not dispute that there is a few percent more to be found! But not double.)

The much bigger problem is that the desire for most people to be safe and comfortable under all conceivable circumstances has resulted in a VW Golf weighing 1400 kg. A secondary problem is that the desire to go from zero to 100 km/h in 8 seconds or less, even if they never drive that way, has resulted in engines that are oversized, and thus don't operate anywhere close to their best BSFC point under ANY normal conditions.

A VW Jetta TDI, or the upcoming Ford Fusion hybrid, is already a 40+ mpg affordable family vehicle. I just found out that the battery in the Fusion prevents the rear seats from folding down ...

60+ mpg seems only realistically achievable with diesel plus at least mild hybrid plus substantial downsizing with reductions in expectations of comfort, safety, or performance. You will not get this from anything the size or weight of a Chevrolet Tahoe (nor even a Malibu).

Look to Europe for the vehicles that meet their 120 or even 100 g/km bogeys. They are out there. It's possible, even today or near-term future. But not in a full-size vehicle.

Stan Peterson

Harvey D,

The ICE has been steadily improved at a rate of 5.3% a year compounded since at least the early Seventies. And more before. See GCC pages

Wringing out these improvements has taken $billions of dollars spent by the World's automakers. They are approaching the last theoretical improvements possible when HCCI arrives, in a few years. To set the stage for that eventuality, most of the enabling technologies, engine control via computerized electronics, turbocharging, DOHC, VVT engines, with GDI, and variable EGR are in place. Each such improvemnt has cost lots of time and money. The last obstacle, reasonable cost, high pressure, fast acting GDI injectors, with long lives and high reliability, are only now arriving on the scene.

The stage is set for HCCI, and hybridization, especially Series hybridization, will maximize the portion of the performance spectrum that HCCI enables.

Governments, emisions and AGW ranters, and safety critics heretofor have merely mandated that the automakers spend on their pet wishes. Without any regard to the costs involved. Any attempt to bring rationality to the scheduel discussion, was transformed into malicious intent and regarded as a desire to kill their customers.

But now they will have to accept the fact that they have bled the automakers too much. If they want more, on a faster, unreasonable schedule, they will have to pay for it themselves.

This novel idea has brought some semblance of reality and sanity back to the most ardent automotive critics.

The average auto exhaust of a new car in LA is BETTER than the average ambient air quality. Stop and think what that statement means. We have come an awfully long way toward cleaning up ICE emission, with only a little more to do. Diesel engines, even when they start arriving in greater numbers, with T2B5 emissions levels mandated for next year, will still need another generation of tightening to achieve T2B3 or better cleanliness. That is still only a mop-up operation, at most.

But there is little necessity to achieve this on a crash basis, any longer. We in the USA alone, among the world's countries, have come so far along the way. By 2025 maybe Europe can catch up and join us.

In practice when given an alternative, most people will not purchase "A" or even smaller "B" segment vehicles. They do so now only because their governments acting "for their own good" force them to seek better fuel economy. I fail to see the difference in whether gouging is performed by government bureaucrat or Oil Shiek, it's stillgouging. It has certainly not resulted in better air quality in the EU. If anything it has gotten worse, with diesel stink and the carcinogens implied, ever more prevalent.

The AGW religious believers do not understand Technology, and think they can just make a wish, and the engineers will produce their desires. Nonsense.

Up to now, better fuel economy, has only been possible by severe downsizing. But not for much longer.
But now that family mid-size cars like the Prius and Ford Fusion, using even primitive hybridization, can achieve 40+ mpg and the EREVs will double that, these tiny cars have little future.

The automotive scene will most certainly be transformed in the next decade.



Thank you for enlighting comments.

Yes, diesel engines have become more efficient and much more cleaner (and not as noisy) at the same time. Automatic transmissions are also gaining in efficiency without getting bigger or heavier. More common size vehicles are coming to the market place without affecting safety.

One improvement does not automatically negate another.

You are right, not everybody needs or wants all the power, accelleration and comfort we have been convinced to buy. Tata-India may produce plainer basic vehicles that more people could affort without going deeper in debt. A low cost basic Tata or BYD BEV with an ESStor supercap ESSU (see US patent no. 7,466,536 B1) could be a game changer.

Brian P

For what it's worth, the Tata Nano (if that's what you are thinking of) doesn't get fantastic mileage, and has not a hope of meeting safety standards in ANY western country, and even if it did, is so basic that scarcely any person in a western country would want one. Given that this vehicle is intended to replace a small motorcycle, and takes up more space on the road and will therefore lead to more congestion, one questions whether this is really progress ... (by the way, my 2007 Honda CBR125R has closed-loop fuel injection and 3-way catalyst, so don't get on me about motorcycles being "dirty", they don't have to be!)

The upcoming Toyota IQ might be more acceptable and useful in western countries, but let's see how the fuel consumption is going to be.

As for the ESStor supercapacitor ... call me a skeptic, but let's see a workable demonstration powertrain before demanding that they be across-the-board in every vehicle. Just because there's a patent, doesn't mean it works. I hope it does, for all the issues they have I recognize that electric is the long-term solution, but all I've heard of regarding ESStor is vaporware.

fred schumacher

This swirl chamber system provides 17% efficiency improvement with no increased cost or complexity in manufacture. The CVCC had an extra valve and other components increasing cost and complexity.

There aren't too many improvements that can provide this much efficiency increase so simply. If polution control components can work with it, it's worth considering.

HCCI has trouble with providing smooth power and response over a large rpm and power output range. This problem can be greatly reduced in a serial hybrid HCCI where power if buffered through a battery pack, which provides variable power supply, while the IC engine acts as a single speed genset. HCCI can then be optimized for that speed. This allows the engine to be greatly reduced in size, since high power demands, except in mountains, tend t be of short enough duration that the storage in moderate battery pack could handle them.


"provides 17% efficiency improvement"
Not quite.
This swirl chamber system is CLAIMED to have "experimentally shown" that it "can" deliver a 17% reduction in fuel consumption with a 7% increase in power compared to a "conventional" 1.6-liter port-injected engine.
Empty words.
What has the Big-3 been doing, indeed.
"Buy stock in Istanbul Technical University (ITU)? Because, if they can ..." ?
No, safer to buy pork futures (for when they fly ...).

Giridhar Raju N M

Interesting indeed, But there is an inherent issue with the above kind of combustion chamber design, they are impressively efficient at a single designed RPM, but across a wide range of speeds like in a Automobile (750 RPM to 12000 RPM )their, performance needs to be seen....

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