dnb

Some of us here go to great lengths to extract more power from engines by various means, mostly requiring more air & fuel to be added. What can be done to increase engine efficiency?

I know that there is the Carnot limit to constrain us a bit, so let's try to keep it practical & implementable...

A couple of ideas for kick off:

1. Using the waste heat to do something useful - no idea what!
2. Keeping the inputs cool.
3. Find a loophole in the laws of physics

[Edited by dnb - 9/26/2003 10:19:58 AM]

leeps

Well ill give my thoughts for what its worth :>

I like the ideas of getting colder air to the intercooler and thus to the engine through those cold air boxes or airconed air ... it seems to be a more cost effective way than a bigger intercooler ...

then it goes without saying that u will probably need to increase fuel somehow depending on your AF ratio and what grade fuel ur using ...

leeps

scoobyslut

I'd of thought that by shoving more fuel into the engine, surely that decreases efficiency? So you have to look at :
1/ increasing air mixture to combustion mix
2/ optimising combustion chamber performance to encourage 100 %
air/fuel burn
3/ Decreasing engine drag loading, cut down on ancillary loads etc,
so for eg: no air con, high power stereo's which create alternator loading, dropping horsepower by at least 4bhp.
4/ Modifying fuel injector spray/injection pattern/pulse, to allow for optimum fuel burn at all engine speeds.

5/ Forget all this and fold the mirrors in and sit lower in the drivers seat and hang the expense of the ever increasing fuel.!!

dnb

scoobyslut - it'll leave efficiency more or less the same, it's just the engine is providing more power.

(Of course adding more fuel for no power benefit will decrease efficiency...)

AJKS

Use a solar panel to drive the aux units... (well in Oz maybe but not the UK).

But in all seriousness...

One of the biggest limiters in engine performance is the compression ratio. I dont mean the static CR which we see listed on specs but the dynamic CR. A conrod streches a certain amount as RPM is increased due to the inertial loading placed on it. Therefore the CR at idle RPM vs max RPM will be different - hence so to will the engines effeciency across the RPM range. This is why race engine builders go to a lot of trouble to lighten all rotating components of an engine (not just to increase the RPM limit) and use titanium conrods etc - to ensure that the CR change across the RPM is at a minimum.

Not to sure if this is the type of thing you were thinking about, but its an idea.

There is some research going on at the moment (and I think Prodrive are also dabbling in it) into 'variable compression ratio' engines - so that the CR can be changed by the ECU across the RPM range.

Another thing you obvisously want to do is limit the amount of combustion energy transfered to 'waste' energy - heat (friction), etc.

adam

Great idea for a thread - love it! Maybe the Webmaster could organise someone from Prodrive to come and have a Q and A session about this (like the one Damian Harty did re vehicle dynamics)...

dowser

Port match everything that has a liquid or a gas flowing through it (paying attention to reversion lips on exhaust). Polish all surfaces of the same. Flow match all multiple branches of the same gas/liquid (ie, inlet manifold [easy] or water bores through block [hard ].
Lighten and balance everything.

Remap to get best results.

Richard

Brit_in_Japan

IMHO there are three main routes to improve efficiency of an engine
1. reduce losses
2. ensure optimum combustion efficiency
3. reclaim "lost" energy, i.e. heat

Losses are predominantly pumping losses and friction. Reducing pumping losses (the work required to suck air in to the combustion chamber and push it out the exhaust) means reducing the resistance to airflow. This is why everyone fits different exhausts and air filters. Internal friction comes from losses in bearings, piston ring to liner and usually the force required to turn the crank through the oil in the sump. Not much you can do by improve efficiency there, bearings and oils are pretty well engineered. Many competition cars are dry sumped, meaning the crank does not sit in a bath of oil, oil is sprayed directly where it's needed. Scoobies have a flat-4 layout, so don't think this gives any new opportunities (but I'm happy to be corrected).

Optimum combustion efficiency - spark plugs, optimimal spark advance. Car companies spend a lot of money looking at combustion chamber designs, wall wetting, swirl etc. Not so easy these days to make gains. Note, combustion wise maximum efficiency and maximum power are not to be found the same place, if you want maximum efficiency you would have to trade it for some performance, and vice versa.

Reclaim lost energy - this is essentially what the turbo does. You use the thermal energy of the exhaust at pressure, expand it through a turbine to recover energy and use that energy to turn a compressor to force more air into the engine. Produces more power but also thermodynamically more efficient. Turbos with intercoolers are thermodynamically more efficient again. If we are just talking about an engine, then recovering more of the rejected heat would be the best new way of improving efficiency. Go invent something.

If you want greater efficiency of the whole vehicle, then look to losses again (aero), regenerative breaking - as per cars like the Toyota Prius parallel electric hybrid (braking turns a generator which charges a battery, to be used to supplement engine when hard acceleration demanded), smaller tyres with less rolling resistance.


Best way to improve efficiency of a scoob, drive around all week in a small modern turbo diesel and just drive the scoob on weekends

dnb

Think no.3 on your list is the one to tackle first. It's the larger of the wasted energies...

Just have to work out what can be done with the heat - it's not like you need central heating and a hot water supply!

DubaiNeil

In response to B_i_J point 1 re crank losses in the oil bath - I recall a number of Evo's running 'knife-edge' cranks, which I presume is planned to reduce the losses in this area.

Obviously the Evo engine layout may lead to more benifits in this area than the Scoob, but just a thought (and probably a darn sight cheaper and easier than dry sump)

For more efficiency in the 'use' of 'free' energy, I would have thought that sequential turbo's would be the most effective approach, if somewhat complex to acheive.
Two different sized turbos, with different VE's, would ensure that the engine would operate in its 'most' eficient zones for more of the time.