Any mechanical engineers in the haus? Help requested!

[jono035]

hmmm, I'm guessing the intake valve on the combustion cylinder is still partially open at TDC to give a high enough compression ratio? I'm kinda struggling to see any benifits over the conventional cycle tbh.

Some of my personal favourites are the steam based 6 stroke and the supercharged two stroke (only diesel so far as can't direct inject petrol yet)

It's a little difficult to visualise because it's so similar to a standard otto cycle engine, but behaves so differently. One of the features they mention is that by separately compressing the input charge air, they can cool it before it enters the combustion chamber, allowing the equivalent of higher compresion.

In the combustion chamber, the intake valve only opens at TDC, at which point the pressure in the crossover chamber (where the compressed air from the other cylinder ends up) is at the compression pressure. The pressure differential means that after a short period the combustion chamber has enough charge in it to start a power stroke so the intake valve closes and the mixture is ignited.

So basically the stroke is TDC-intake-ignition-power-BDC-exhaust-TDC.

It's a neat idea, and I like it because of the novelty but it certainly seems to have a few design challenges associated with it.

One of the main advantages they mention is that basically it can be considered as a separate compressor and 'combustor', allowing a large air reservoir to be placed between them. This means that a certain amount of energy can be regenerated while braking by disabling the combustor cylinder (by simply leaving both valves closed, similar to existing cylinder-disabling tech) and using the compressor to raise the pressure within an air tank. This energy can then be 'retrieved' by disabling the compressor and only running the combustor. That's the only way that I've heard of to do regenerative braking entirely within a petrol engine (i.e. doesn't require an electric drivetrain). There was a mention of it being a possibility with good enough valve timing control to even use an air tank to run the thing entirely on the compressed air without any combustion at all for a short period of time.

I've seen that 6 stroke thing mentioned before, very interesting idea.

[Slyer]

So have we answered the question? Yes, there are mechanical engineers in the haus.

[bogan]

hmmmm, the intake valve will be open so briefly as to become a design/rpm constraint I reckon. Also storing energy in a tank also means storing petrol vapor in there as well, which would condense out wouldn't it? The supercharged two stroke direct injection design does all this without the valve constraints, or compressed vapor issues. And with orbit's apparent breakthrough allowing direct injection of petrol (albeit with a bunch of air) perhaps the design could be made to work with petrol.

[jono035]

hmmmm, the intake valve will be open so briefly as to become a design/rpm constraint I reckon. Also storing energy in a tank also means storing petrol vapor in there as well, which would condense out wouldn't it? The supercharged two stroke direct injection design does all this without the valve constraints, or compressed vapor issues. And with orbit's apparent breakthrough allowing direct injection of petrol (albeit with a bunch of air) perhaps the design could be made to work with petrol.

Could very well become a design/rpm constraint, although it will be an ultimate-power-output constraint, not necessarily an efficiency constraint which is what they're shooting for primarily. I believe they are injecting into the air-stream right before the valve, using the swirl over the valves to ensure an even charge density.

It's not that dissimilar to the idea of a supercharged 2-stroke. I'm sure there are a lot of advantages that are shared between them.

Also, none of this is an all-or-nothing type approach. There may be merits to both and specific advantages/disadvantages that make each one more or less useful for any given example. Both could end up being useful for entirely different purposes.

The ability to use the compressed air as a block of regenerative storage is an interesting one though. Could also possibly be used to provide for other systems such as power steering etc. if the intake compressor was sized to have a longer stroke than the combustor or something.

[jono035]

So have we answered the question? Yes, there are mechanical engineers in the haus.

Don't look at me, I'm an electrical kinda guy, the mechanics quickly leaves me baffled.

[bogan]

The ability to use the compressed air as a block of regenerative storage is an interesting one though. Could also possibly be used to provide for other systems such as power steering etc. if the intake compressor was sized to have a longer stroke than the combustor or something.

have you seen the modded ducati which uses the rear cylinder to supercharger the front one? ended up making slightly more power than stock I think, it uses a charge tank for engine braking I think, which is a fantastic idea as you can run on tank air for brief acceleration bursts without any hp losses associated with running a supercharger.

[bogan]

Don't look at me, I'm an electrical kinda guy, the mechanics quickly leaves me baffled.

I'm a mechatronics major, means everything only leaves me slighty baffled

[jono035]

have you seen the modded ducati which uses the rear cylinder to supercharger the front one? ended up making slightly more power than stock I think, it uses a charge tank for engine braking I think, which is a fantastic idea as you can run on tank air for brief acceleration bursts without any hp losses associated with running a supercharger.

No, I'll have to take a look around for that, that's very interesting...

[bogan]

http://thekneeslider.com/archives/20...le-conversion/ there ya go, the ducati v-one

[schrodingers cat]

Don't look at me, I'm an electrical kinda guy, the mechanics quickly leaves me baffled.

electrics is all just pipes and smoke. If you kink the pipes the smoke comes out and it doesn't go.

Thats how I understand 'white-mans magic' anyhoo

[motorbyclist]

thats easy, two! in a V configuration though

nah, v-four ftw

Slyer: Interesting, wasn't aware of that, that's a weird crank angle too, to get a big-bang firing order, isn't it.

it's to get a v4 firing order with appropriate exhaust note

Correct - an internal combustion engine is only 25 - 30% efficient due to heat rejection.
.

IIRC the human digestive system was marginally more efficient than an ideal carnot cycle (which was only a maximum of 35% or something given a typical four stroke)

So have we answered the question? Yes, there are mechanical engineers in the haus.

actually, we're all mechatronics or electrical or not engineers at all..... of course it's pretty hard to find automotive engineers in this country at all and they're all working on bio-diesel or similar as that's all there's funding for at the moment

the mechanical guys are all doing structural stuff, manufacturing (not the cool part that the 'tronics guys do) or HVAC.

HVAC. Heating, ventilation and air conditioning. woo hoo

have you seen the modded ducati which uses the rear cylinder to supercharger the front one? ended up making slightly more power than stock I think, it uses a charge tank for engine braking I think, which is a fantastic idea as you can run on tank air for brief acceleration bursts without any hp losses associated with running a supercharger.

long story short, they went from 84hp all the time, to around 40hp most the time (ie around most IL4 250 bikes) and 100hp for ten seconds.

begin rant

i'm a bit annoyed about that:

for one, that motor was pretty lame anyway; I'd be interested to see what it does given some basic performance work without the supercharger (ok, maybe major work considering it has only 2 valves per cylinder). you'll note their new claimed power output has a redline 30% higher than the stock arrangement, without mentioning modification to the belt driven desmo two valve. Surely they should have dyno'd the stock motor tuned to run at that speed too? Otherwise how much power was the charger and how much was due to the revs?

next, heat; it's air cooled with a tiiiny oil cooler, and the working cylinder has had it's power output more than doubled. how do they deal with the extra heat? ie how long can this run under boost?

volumetric efficiency; the dragging cylinder won't help without major work. It physically can't as its pumping the same air the firing cylinder would suck anyway with extra valves to hinder the flow. The only way this would work is with in a 2 stroke arrangement with significant overbore, which required reed valves or re-engineering the cams and rockers to run at double speed.

the fine print; they run an air tank under the seat at 40bar to give a ten second boost. The "supercharger" is only really there to pump up the tank to give boost. ie, their power claim will be with the boost on as high as they dare to run it. safety issues aside, there ARE pumping losses associated with that supercharger simply to pump that presssure, plus they lost a cylinder to drive it!

so 95% of the time they're pulling less than half the stock motor power, except for brief, intermittent bursts where the motor is well past it's limits and will probably seize given any longer boost time. and the more often you want the boost the harder you're going to have to pump the compressor, which means less power the rest of the time

they may as well have removed the dead cylinder entirely and fitted a normal, purpose built supercharger in it's place. Maybe even re-worked the ducati electrics with a heavy duty charging system and run an electric super instead? Heck, why not fit an appropriately sized turbo?
If you want to avoid supercharger losses when wyou don't want the power, just use a clutch!

/rant

[jono035]

nah, v-four ftw



it's to get a v4 firing order with appropriate exhaust note



IIRC the human digestive system was marginally more efficient than an ideal carnot cycle (which was only a maximum of 35% or something given a typical four stroke)




actually, we're all mechatronics or electrical or not engineers at all..... of course it's pretty hard to find automotive engineers in this country at all and they're all working on bio-diesel or similar as that's all there's funding for at the moment

the mechanical guys are all doing structural stuff, manufacturing (not the cool part that the 'tronics guys do) or HVAC.

HVAC. Heating, ventilation and air conditioning. woo hoo



long story short, they went from 84hp all the time, to around 40hp most the time (ie around most IL4 250 bikes) and 100hp for ten seconds.

begin rant

i'm a bit annoyed about that:

for one, that motor was pretty lame anyway; I'd be interested to see what it does given some basic performance work without the supercharger (ok, maybe major work considering it has only 2 valves per cylinder). you'll note their new claimed power output has a redline 30% higher than the stock arrangement, without mentioning modification to the belt driven desmo two valve. Surely they should have dyno'd the stock motor tuned to run at that speed too? Otherwise how much power was the charger and how much was due to the revs?

next, heat; it's air cooled with a tiiiny oil cooler, and the working cylinder has had it's power output more than doubled. how do they deal with the extra heat? ie how long can this run under boost?

volumetric efficiency; the dragging cylinder won't help without major work. It physically can't as its pumping the same air the firing cylinder would suck anyway with extra valves to hinder the flow. The only way this would work is with in a 2 stroke arrangement with significant overbore, which required reed valves or re-engineering the cams and rockers to run at double speed.

the fine print; they run an air tank under the seat at 40bar to give a ten second boost. The "supercharger" is only really there to pump up the tank to give boost. ie, their power claim will be with the boost on as high as they dare to run it. safety issues aside, there ARE pumping losses associated with that supercharger simply to pump that presssure, plus they lost a cylinder to drive it!

so 95% of the time they're pulling less than half the stock motor power, except for brief, intermittent bursts where the motor is well past it's limits and will probably seize given any longer boost time. and the more often you want the boost the harder you're going to have to pump the compressor, which means less power the rest of the time

they may as well have removed the dead cylinder entirely and fitted a normal, purpose built supercharger in it's place. Maybe even re-worked the ducati electrics with a heavy duty charging system and run an electric super instead? Heck, why not fit an appropriately sized turbo?
If you want to avoid supercharger losses when wyou don't want the power, just use a clutch!

/rant

Well in terms of 'pumping losses', a normal engine has those anyway, and if everything were perfect, the rear cylinder pumping full capacity every cycle and then that being solely fed into the front cylinder would result in the same total airflow, with the same total 'pumping loss' with the same total output power because the same total petrol is being burned.

Of course, it won't work out like that but it doesn't seem all that far off.

I certainly think that they'd pick up the extra 16 HP with tweaking to the original engine, but I like the idea nonetheless.

Also, 40hp is enough to keep you moving at 100km/hr so with some modification to be able to entirely shut off the pump once the tank is full, it could end up having similar performance (boosted single cylinder for accel, N/A single cylinder for cruising) to the original bike under cruising conditions.

Assymetrically sized cylinders could be an interesting one too.

All in all, an interesting exercise but I would have expected an engineer student to be a bit more in tune with people doing things like this 'because they can'.

[bogan]

All in all, an interesting exercise but I would have expected an engineer student to be a bit more in tune with people doing things like this 'because they can'.

indeed, though the article was pretty biased by the sounds of it, pity that.

also worth adding that the stock wouldn't have made more power at higher revs as without any forced induction it wouldn't get a significant amount of air, thats why the modded engine runs higher rpm.

Still a cool idea to use existing equipment to supercharge the engine, though when it boils down to it, its a supercharged engine with half the cc, can't expect too much.

[schrodingers cat]

note

IIRC the human digestive system was marginally more efficient than an ideal carnot cycle (which was only a maximum of 35% or something given a typical four stroke)

Ewwwwwwwww interesting.

So here's another question - whilst food is a 'renewable resourse' by the time it gets on our plate it has had a good deal of carbon expended on it (Production, processing, storage, distribution, preparation)

Which energy source is more efficient in a total sense - 100 000 calories of diesel or 100 000 calories of food?

Maybe the lentil eating (methane farting) treddly greenies should shut the fuck up about how great the bicycle is. After all - the majority of bicycles aren't carved from wood are they? There is a whole industry supporting bicycles - just like cars and motorcycles.
It is a product of the industrial revolution with all its inherant problems.

[jono035]

I'm not sure what's worse, incoherent ranting greenies or incoherent anti-greenie ranting...