Dirty exhaust gases could make cars cleaner - COOL! - GreenHybrid

lars-ss · #1 (**permalink**) 09-22-2005, 08:15 AM

http://www.easier.com/view/News/Motoring/article-28431.html

This is a very promising (at the outset) invention that if pans out could be great for the environment and fuel emission pollution reduction.

Quote:

The British engineers have developed a simple but revolutionary way of recovering energy that would normally be lost down the exhaust pipe. The exciting ‘free power’ breakthrough has three key green benefits – it makes engines more efficient, reduces emissions and creates enough electricity to run all of a car’s power systems.

And, because the technology is fairly simple, it could be fitted on all car, van, bus and truck engines within a few of years.

It could reduce fuel consumption by up 10 per cent and help hit the Government’s commitment to reduce greenhouse gas emissions. But engineers working on the TIGERS project under the Society of Motor Manufactures and Traders Foresight Vehicle research initiative, say this is only the beginning.

So, how does it work? Just below the manifold, where the exhaust system joins the engine, the engineers have installed an extra waste pipe. A valve, linked to the engine’s management control system, allows some of the high energy gases to be drawn off to drive a special generator, using a device called a switched reluctance drive (SRD).

Because so much energy is tied up in the high temperature exhaust gas, that can reach 130mph, it can spin the generator at up to 80,000 rpm and creates an electrical power of up to 6kW – more than enough to drive a car’s electrical systems.

AZCivic · #2 (**permalink**) 09-22-2005, 10:03 AM

It was also shown over in this story at greencarcongress yesterday. The picture shows a visual for how they avoid the usual problem of turbo's only operating efficiently in a certain range of exhaust flows. The Tigers system seems to be geared towards recapturing energy from very low exhaust flow and rather than becoming a restriction at higher load and engine speeds, it lets the majority of exhaust gas bypass it entirely. Pretty cool system. At elevated road speeds (perhaps 45-50mph) there would likely be sufficient exhuast flow to efficiently recapture enough waste heat energy from the exhaust to fully charge a hybrid's battery pack with no drag on the engine.

Once the battery pack is at acceptable charge, the Tigers could then divert power towards supplementary propulsion, further reducing the amount of gasoline used even at highway speeds. This has always been one of the weak points for hybrids - the electric assist and battery pack are of little or no use when cruising at 75mph on a flat highway for hours at a time. With the Tigers system, you're recapturing a huge amount of waste energy from the exhaust and can use it to provide a constant 6kw of primary propulsion, in theory, thus improving highway fuel economy greatly.

clett · #3 (**permalink**) 09-22-2005, 04:09 PM

Just to clarify, the device isn't designed to capture waste heat energy from the exhaust gas, it will be capturing the kinetic energy of it as it flows through the exhaust pipe. I am a little concerned therefore that the increased exhaust resistance arising from installing the device may increase pumping losses in the engine accordingly (ie the engine will have to work harder to push the exhaust gas down the pipe), thereby using more fuel to run it. Would be nice to see some figures from a demo vehicle....

Having said that, though, there is still such a thing as a free lunch. You can extract a heck of a lot of energy out of the hot exhaust gases by doing something very simple - letting the piston expand a bit further for a bit longer. The expansion stroke does more work, pushing the piston for longer and more of the energy of the fuel goes into mechanical motion (while the exhaust gases gets cooler).

For example, a typical gasoline engine (25% efficient) has an expansion ratio of 10:1, but the Prius Miller cycle engine has an expansion ratio of about 13:1 giving it an efficiency of up to 35%. Going the diesel route is even better, with many road engines approaching 20:1 and efficiency up to 45%. Marine diesel with longer expansion strokes can get over 50% efficient.

phoebeisis · #4 (**permalink**) 09-22-2005, 07:50 PM

This is a great idea.I'm sure it is an old idea,but I'm guessing it is now feasible because there are now tiny turbines with very low resistance bearings.
Prior to hybrids becoming popular the only good way to capture wasted exhaust energy was to use it to turbocharge a small engine,and make it act like a "big engine".Unfortunately spark ignition engines can't really benefit much from turbocharging;they are very prone to detonation at over 5 PSI boost.With a Hybrid the wasted gas velocity can now be used to charge the batteries and run the electric motors.6KW is about 8 hp.8 HP could probably push a Prius at a steady 30 miles per hour.
A Gasoline Hyrid equipped with this gadget could probably match a TDI Hybrid in mpg,and it would be cheaper and lighter than a TDI hybrid.
Back pressure shouldn't be a problem.If there is a bypass used it won't increase backpressure at all,and you could probably decrease muffler weight and volume since the turbine will drop the sound energy a lot.Great.Charlie