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Novel, high-efficiency exhaust systems
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NASkeet
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PostPosted: Tue Mar 18, 2008 7:28 am    Post subject: Novel, high-efficiency exhaust systems Reply with quote

Here is an interesting journal article I came across, whilst browsing my university library's current-issue, journal & magazine rack, when I was a postgraduate student of Applied Energy Engineering, at the Cranfield Institute of Technology, during 1979~84.

It examines a novel, high-efficiency tubular exhaust system, as an alternative to the conventional 4-1 or 4-2-1 tubular exhaust system. It's certainly a practical option, for four-cylinder, in-line engines, but I have often wondered how one could implement such a design, for four-cylinder, horizontally-opposed (i.e. flat-four or boxer) engines.

David Scott, "Venturi exhaust boosts extraction, cuts consumption", Automotive Engineering, Volume 91, Number 4, April 1983, pages 58~59.

VENTURI EXHAUST BOOSTS EXTRACTION, CUTS CONSUMPTION

A multi-pipe exhaust system under development in Britain by Hansen Engines uses gas flow from a fired cylinder to produce pressure-wave scavenging for anoother cylinder with which it is paired. This ejector arrangement reduces the work needed to expel burned gas from the second cylinder, and is reported to improve fuel consumption and engine tractability.

Each exhaust port feeds two manifold pipes, where flow is equally divided. While both pipes ultimately discharge into the main outlet, one is initially subject to a depression that drops cylinder pressure when the exhaust valve opens. The connections are shown in the accompanying diagram.

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Given a four-cylinder engine with standard 1-3-4-2 firing order, cylinders Nos. 1 & 3 are coupled in this way, as are Nos. 3 & 4, 4 & 2, and 2 & 1. Thus when No. 1 starts exhausting, No. 3 is starting its power stroke. As the latter piston reaches BDC its exhaust valve opens to a negative pressure in one outlet pipe. This is created by a venturi effect in the converging collector box, where the steep-fronted pressure pulse from No. 1 is followed by a suction wave. The other paired cylinders provide mutual extraction in the same phased relationship.

Hansen claims a 25% improvement in exhaust gas extraction with the system at its early experimental stage, and estimates that 60% might be possible with further development. Chassis dynometer tests with a Ford Cortina powered by a 1600cc pushrod engine, independently conducted by Ricardo Consulting Engineers, gave a 20% reduction in consumption on the European ECE15-04 cycle.

Economy gains were somewhat less at a steady 40, 50 & 60 km/h, and there were none at 90 km/h. NOx and CO emissions were measurably reduced on the European tests, though HC were higher across the board, possibly due to lower combustion temperatures.

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These results were obtained with no alterations to carburettor or ignition settings. Subsequent tests, however, showed a 10% to 15% loss in power with these original settings, apparently caused by an over-rich mixture resulting from the better scavenging of exhaust gases. Power was then restored to the original level by fitting smaller jets to the Weber carburettor, giving a lean-burn mixture. While the manifold gave no power increase, vehicle performance benefitted from faster acceleration due to reduced engine pumping loads during exhaust cycles.

Turbocharging is not thought to be applicable with this exhaust system, since the lowered final gas velocity would probably be inadequate to drive the turbine at its required speed. However, such an alternative form of utilizing waste energy with no moving parts could perhaps provide comparable acceleration gains, and at a fraction of the cost, it is claimed.

The company envisages the new manifold concept as part of a fresh approach to exhaust gas extraction., which it views as a major obstacle to greater fuel efficiency. A second stage, still only on paper, would be two-stoke exhaust porting incorporated in a four-stroke OHV or OHC engine. Small ports around the edge of a pisto's bowl-in-crown combustion chamber communicate via tubes passing through the cylinder wall and water jacket to an external gallery.

They would be uncovered when the piston reaches BDC, and relieve gas pressure at its maximum point through the base of the cylinder combustion section. The gallery outlet pipe, bleeding off this high-velocity gas, is coupled by a collector box to the pipe from the normal exhaust poppet valve above, which now opens.

Depression created in the upper pipe by the venturi effect would then assist gas flow through the valve as before. Although piston ports would also be uncovered at the bottom of the inlet stroke, it is thought that negative pressure within the cylinder following induction would inhibit passage of the charge mixture through these openings. The piston bowl would be contoured to enhance charge containment, while the exhaust pipes would require special tuning to prevent ingress of residual burned gas.

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Jonathan Beard, "Manifold blessings: Just because it's fast doesn't mean it can't be green", New Scientist, 20th March 1999, page 5.

http://www.newscientist.com

It's a car maker's dream: an engine with increased power but lower emissions. And all it took were some holes drilled into its exhaust system.

Ahmet Selamet of Ohio State University in Colubus, working with engineers at the Ford Motor Company near Detroit, has been looking at the problems car engines have in trying to force gases down the exhaust manifold - the converging pipes that carry exhaust gases away from the cylinders towards the catalytic converter. Gases entering the manifold create back pressures that decrease an engine's efficiency.

The pressure waves formed as gases emerge from the cylinders also generate deafening noise - upto 190 decibels at the input to the manifold. "This is why cars have complex muffling systems", says Selamet.

Selamet and his Ford colleagues have enclosed a manifold within casing and redesigned the tubes or "runners" so that the lead the gases away from the engine more smoothly. Each runner is perforated with about 200 holes less than 3 millimetres in diameter.

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Only a small amount of exhaust gas actually escapes from the runners into the outer casing. But it is enough to dissipate the offending pressure waves. "The perforations make it seem that the gases are expanding into a much larger volume", says Selamet. In tests, the new manifold cut the back pressures in the exhaust system enough to boost the engine power by between three and five percent.

The engineers also moved the catalytic converter closer to the engine than usual. This means it heats up more quickly after the engine is started. "Most of the emissions come in the first few minutes of driving, before the catalyst heats up", Selamet explains. "By close-coupling the converter to the engine, it begins working faster". Tests on a 1•9 litre Ford Escort engine showed that emissions of nitrogen oxides, carbon monoxide and hydrocarbons were reduced by 9, 16 & 37 percent respectively.

Kris Norman of Ford, who worked with Selamet, says that the design could be used on any internal combustion engine. The pressure-wave reduction could allow exhaust designers to use simpler silencers. "Because of the sound reduction, we can eliminate many of its baffles", he says.

Ford has applied for a patent on the exhaust design, which it calls the Perforated Manifold, Muffler & Catalyst exhaust system.

**************************************************************************************************************************

Rachel Nowak, "Little gem: It will cut your car's emissions and make diamonds as you go", New Scientist, 7th October 2000, page 11.

Australian engineers have invented a device that blasts the noxious gases in car exhausts with microwaves, eliminating upto 70 percent of harmful emissions. Better still, the process can double as a source of industrial-grade diamonds.

Their device, called a microwave emissions converter, is about the size of a wine bottle. It microwaves the exhaust gas, heating its core to as much as 5,000 Kelvin (i.e. 9,000 degress Rankine; equivalent to about 4,727 ºC or 8,541 ºF), more than three times the melting point of steel. At this temperature, molecular bonds in the gases break, creating a plasma of free ions.

As the mix cools, the ions recombine to form less harmful substances. "Under ideal lab conditions, we get 90 percent reduction in carbon monoxide, carbon dioxide and hydrocarbons. On the road, it will probably fall to around 70 percent", says Elias Siores at Swinburne University of Technology in Melbourne, who developed the converter with Carlos Destefani. They have filed a patent on the device.

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Although the converter works on diesel and petrol engines, and can be used downstream of a catalytic converter to further reduce emissions, it has a downside. It increases the number of tiny carbon particles spewed out in the exhaust. To combat this, the pair have developed a way of harvesting the carbon and producing industrial diamond from it.

An electrostatic filter lining the exhaust pipe attracts the carbon particles. These particles are collected and used to feed a separate process called microwave plasma spray deposition, in which microwaves heat up and ionise an inert gas such as argon or helium. The ionised gas reacts with the carbon to create a volatile liquid. This is then sprayed onto a glass surface, producing industrial-grade diamond.

"Every time you have your car serviced, you'd have the filter taken out and it would be sent to the factory and used to make industrial diamond", says Siores. "The diamond could be used as a protective coating for lenses, CDs, artificial hip joints, and electronic components", he says.

If their prototype makes it to the production line, cleaner exhausts would have an immediate impact on people's health, and help cut levels of greenhouse gases.

The same technology could be used to clean up emissions from factories, chemicals plants and power stations. "There are lots of manufacturing processes that give off hydrocarbons. We are going to look at using this technology to reduce these", says David Galvin, executive director of the Cooperative Research Centre for Intelligent Manufacturing Systems & Technologies in Melbourne.
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Independent tutor (semi-retired) of mathematics, physics, technology & engineering for secondary, tertiary, further & higher education.

Much modified, RHD 1973 VW "1600" Type 2 Westfalia Continental campervan, with the World's only decent, cross-over-arm, SWF pantograph rear-window wiper

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Last edited by NASkeet on Wed Mar 19, 2008 7:30 am; edited 1 time in total
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mharney
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PostPosted: Tue Mar 18, 2008 8:09 am    Post subject: Reply with quote

Indeed.
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krusher
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PostPosted: Tue Mar 18, 2008 8:17 am    Post subject: Reply with quote

Did any of these ideas ever make it onto a production car?
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PostPosted: Tue Mar 18, 2008 9:11 am    Post subject: Reply with quote

The problem with the VW motor is that it does not fire from one side then the other. both cylinders fire on each bank. This is why the 4-1 header is so popular. Works quite well as an extractor when designed correctly. It is also why the centermount carb is not such a good choice.
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NASkeet
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PostPosted: Tue Mar 18, 2008 9:11 am    Post subject: Novel, high-efficiency exhaust systems Reply with quote

Jimmy111 wrote:
The problem with the VW motor is that it does not fire from one side then the other. both cylinders fire on each bank. This is why the 4-1 header is so popular. Works quite well as an extractor when designed correctly. It is also why the centermount carb is not such a good choice.


The 4-1 exhaust manifold, is best suited to maximising top-end power, whilst the 4-2-1, is better for low & mid-range power, which is more appropriate for road cars, especially the VW Type 2.

krusher wrote:
Did any of these ideas ever make it onto a production car?


That, I do not know, but they're interesting none the less!

Sometimes, optimum-efficiency components or systems, fail to go into production, because they cannot readily be produced economically, on a production-line basis, but can only be fabricated using craft technology.

I believe this happened with British Gas's 100% efficient gas burner!
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Regards.

Nigel A. Skeet

Independent tutor (semi-retired) of mathematics, physics, technology & engineering for secondary, tertiary, further & higher education.

Much modified, RHD 1973 VW "1600" Type 2 Westfalia Continental campervan, with the World's only decent, cross-over-arm, SWF pantograph rear-window wiper

Onetime member, plus former Technical Editor & Editor of Transporter Talk magazine
Volkswagen Type 2 Owners' Club (Great Britain)

http://www.vwt2oc.net
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