Article: adding a turbo to improve efficiency

[diesel_john]

Here is an article on diesel turbo technology. I get the impression they want power more than economy.
http://www.sae.org/servlets/newslett...4&PID=25050132


Thought about putting a Smoky homogenizer on the vw, but without the boost feedback to the injection pump. So instead of adding fuel as the boost increases, limit fuel to control boost and just recycle some of the heat and eliminate the muffler.

Would higher intake temp. on a diesel be like reducing the compression ratio?

Fuzzy getting back to your question. "It'd be nice to have more information on how to correlate common turbo specifications to an engine size in order to accomplish these kind of goals."

I contacted a friend who designed turbos and this was his reply.

"Matching Turbos is somewhat science and art (trial and error). It helps to
have a waste-gated turbo but you still have to match the engine flow rates
at different speeds with the turbine and compressor flow maps. You don't
want the flows to run off the component maps.
A book which goes through the matching techniques.
Authored by Hugh MacInnes.
But even with that info you still need the turbo component maps for the matching."

[LostCause]

Originally Posted by LostCause

First, take a small atkinson cycle engine - 13:1 CR with an effective 8:1 CR. Use a small, efficient turbo ducted through an intercooler to raise the effective CR to ~10:1 (i.e. miller cycle). Use variable valve timing to increase the CR to 13:1 w/ turbo (which should already be operating in its most efficient range) and switch the injectors over to feed from a smaller tank holding 91 - 100 (avgas?) octane fuel during acceleration. Route the spent gasses through the primary turbo and feed the residual gas into a turbocompound that sends power back into the flywheel.

I don't mean to quote myself, but this will put my response into context. I always think it's cool when some of the crazy ideas I think up get validated by a legitimate group. I suppose it's because it's the logical conclusion to a problem, but at least I don't feel like a total crackpot dreamer...

Anyways, I stumbled upon this. MIT developed a small turbocharged engine that uses direct-injection of ethanol for acceleration to combat detonation in a normal SI engine. 1 gallon of ethanol supposedly lasts 100 gallons of gasoline. While it's not 100LL, it is the same concept. No mention of the VTEC Miller Cycle though, .



BTW, the same thing happened with BMW's steam cycle using waste heat. I figured why not use the already hot coolant, super heat a portion of it, inject it into cylinders or an integrated steam engine (like Honda's IMA). Free energy for a little complexity, woo hoo.



Another idea is evaporative cooling. An old 1930's concept of using the latent heat of water to cool an engine. Pressurized water (coolant runs at ~5psi right now I believe, but this would need more) is heated well above boiling and evacuated into a tube at atmospheric pressure. Liquid water --> steam sucks up tons of energy in itself and steam has a lower specific heat capacity. I remember seeing this online for cars somewhere, the idea being to lower the cooling system weight and drag...

Sexy...


Hmm, now what about my flying robot ninja idea...or training galapagos turtles as a form of alternative transportation...yeah...

Originally Posted by diesel_john

Would higher intake temp. on a diesel be like reducing the compression ratio?

Compression ratio is a geometric quality determined by initial and final cylinder volume. A higher intake temp would kill power as it would be less dense. Less air = less fuel = less power. Higher temps would serve to evaporate fuel and encourage complete combustion, but you gets tons of NOx (chemical smog + major greenhouse gas) and you could, although unlikely, run into metallurgical issues w/ exhaust valves overheating.

- LostCause

[diesel_john]

but the air fuel ratio on the diesel can be as high as 200 to 1. so at light loads i am pumping a lot of extra air for no reason.

what i want to do is reduce the effective displacement at light loads.

[LostCause]

Good point. Diesels, especially the passenger variety, are a bit of a black art to me. I'm pretty sure diesels can operate without a throttle plate, but I'm assuming your car has one. I'm also assuming that your car uses mechanical injection. If that is the case, I'm wondering how it meters the fuel?

I'd like to understand your reasoning for wanting to run a HAI. As far as I know, lowering the effective displacement will only be beneficial by making your engine "work harder" to maintain speed. What I mean is that the throttle plate will be at full throttle (fully open) to limit pumping losses. If you have control over fuel metering, then lowering the amount of fuel injected will accomplish the same thing since stoichiometry isn't a limiting factor.

Even though hot air is less dense, it is also more viscous. This may cause increased pumping losses, I'm really not sure though...

EGR is only useful for lowering combustion temperatures, so I don't see how routing the muffler to the engine will increase efficiency. Too much EGR and you also have combustion issues. I'd like your feedback.

- LostCause

[s2man]

Originally Posted by LostCause

I always think it's cool when some of the crazy ideas I think up get validated by a legitimate group.

Yeah, it always feels good when an "expert" agrees with you. I was designing a 10HP diesel over hydraulic car a long time ago, and everyone was laughing at me. Then one of my industry magazines had an article on converting buses to diesel/hydraulic hybrids. Then folks didn't think I was so crazy.

[RH77]

I thought I'd resurrect this thread with some MAP questions.

After a few hundred miles of observing the MAP figure on the SG, of course decel = lower numbers and higher FE, and accel = higher numbers, lower FE. Just brainstorming, it is possible reduce the manifold pressure at higher RPMs, and still maintain stoich? I'm not sure how you would do that without increased vacuum or some such.

...or is MAP a result of what is happening, and cannot be manipulated unless forced induction is added to increase the figure, and negate FE gains?

...just brainstorming engine functions...

RH77

[LostCause]

Originally Posted by RH77

I thought I'd resurrect this thread with some MAP questions.

After a few hundred miles of observing the MAP figure on the SG, of course decel = lower numbers and higher FE, and accel = higher numbers, lower FE. Just brainstorming, it is possible reduce the manifold pressure at higher RPMs, and still maintain stoich? I'm not sure how you would do that without increased vacuum or some such.

...or is MAP a result of what is happening, and cannot be manipulated unless forced induction is added to increase the figure, and negate FE gains?

I'm not sure what you mean buy "higher numbers" and "lower numbers." I take it you mean lower numbers as closer to atmospheric and higher numbers as higher vacuum...

Ideally, you don't want to pull a vacuum at all. It requires energy to create a vacuum, which is expressed as pumping losses. Pulling high vacuum during acceleration is a result of a nearly closed throttle plate. It's like the engine is sucking through a straw.

I believe part of the reason why "Atkinson cycle" engines are so efficient is that pumping losses are heavily reduced. Charged air is sent back into the intake manifold destroying the vacuum. The same can be done with a supercharger (whether it be turbine or engine-powered).

The killer determination is figuring out whether the method of destroying that vacuum absorbs less energy then the formation of the vacuum in the first place. If it absorbs more energy, you're wasting your time.

BTW: Technically, if you are using a "supercharger" to bring MAP to ambient, it isn't a supercharger.

supercharger: a compressor that brings MAP > 1 atm
turbosupercharger: a compressor that brings MAP > 1 atm via a turbine
normalizer: a compressor that brings MAP = 1 atm
turbonormalizer: a compressor that brings MAP = 1 atm via a turbine

Generally, normalizers are used on aircraft piston engines to combat the effects of decreased density with altitude.

- LostCause

[RH77]

Originally Posted by LostCause

I'm not sure what you mean buy "higher numbers" and "lower numbers." I take it you mean lower numbers as closer to atmospheric and higher numbers as higher vacuum...

Lower MAP figures = lower than ATM, which I assume is considered a vacuum of sorts. My question: when lifting from the accelerator, vacuum is apparently produced, and (assuming the injectors are not cut), FE increases per the gauge.

Ideally, you don't want to pull a vacuum at all. It requires energy to create a vacuum, which is expressed as pumping losses. Pulling high vacuum during acceleration is a result of a nearly closed throttle plate. It's like the engine is sucking through a straw.

So acceleration closer to ATM is more efficient? This generally happens during WOT -- where the forced induction comes into play in non-WOT applications.

I believe part of the reason why "Atkinson cycle" engines are so efficient is that pumping losses are heavily reduced. Charged air is sent back into the intake manifold destroying the vacuum. The same can be done with a supercharger (whether it be turbine or engine-powered).

The killer determination is figuring out whether the method of destroying that vacuum absorbs less energy then the formation of the vacuum in the first place. If it absorbs more energy, you're wasting your time.

BTW: Technically, if you are using a "supercharger" to bring MAP to ambient, it isn't a supercharger.

supercharger: a compressor that brings MAP > 1 atm
turbosupercharger: a compressor that brings MAP > 1 atm via a turbine
normalizer: a compressor that brings MAP = 1 atm
turbonormalizer: a compressor that brings MAP = 1 atm via a turbine

Generally, normalizers are used on aircraft piston engines to combat the effects of decreased density with altitude.

- LostCause

Still, we're only at the theory stage with this sort of inquiry. I recall a couple years back hearing of a guy with a Civic that ran 0-psi of boost from a turbo to reduce pumping losses or something similar.

Basically, I need more efficient, operability in the low RPM range (1500-2500).

RH77

[diesel_john]

the manifold absolute pressure sensor on the Ford speed/density system outputs a frequency proportional to manifold absolute pressure.
engine idle about 100 Hz
engine wide open about 157 Hz

[LostCause]

Originally Posted by RH77

Lower MAP figures = lower than ATM, which I assume is considered a vacuum of sorts. My question: when lifting from the accelerator, vacuum is apparently produced, and (assuming the injectors are not cut), FE increases per the gauge.

The only reason I can think of is that your engine is producing less HP when you lift the gas pedal. Lets say that during acceleration @ 45mph you are pulling 65HP, but cruising @ 45mph requires 15HP. Logically, less fuel is going to be consumed cruising than accelerating at a given speed. I don't think the arrival of vacuum is any benefit.

So acceleration closer to ATM is more efficient? This generally happens during WOT -- where the forced induction comes into play in non-WOT applications.

Driving with load is generally the most efficient, not necessarily accelerating. The idea is to keep rpm's low, but throttle demand high. I don't think the intake manifold ever sees 1 atm, though, so forced induction could still be useful while driving with load.

Forced induction would serve as a band-aid rather than a solution, in my opinion. Essentially, a constriction is being overcome with brute force (which requires additional energy). The most elegant solution would be to remove the constriction.

Still, we're only at the theory stage with this sort of inquiry. I recall a couple years back hearing of a guy with a Civic that ran 0-psi of boost from a turbo to reduce pumping losses or something similar.

Basically, I need more efficient, operability in the low RPM range (1500-2500).

RH77

I operate at the theory stage...

To gain low-rpm functionality, you either have to increase complexity or compromise. If neither option is desired, low-rpm efficiency can just be avoided via pulse and gliding.

In order of difficulty (easy --> hard).

• Create a new intake manifold with runners sized for low-rpms. By timing the intake pulses to coincide with valve overlap you increase cylinder scavenging...and consequently lower the effect of high vacuum. Without variable length intake runners, you'll hurt mid/top-end performance.
  .
• Add an oversized turbocharger with the wastegate set for 1 atm. This might be tough as I know piston-engine aircraft use a totally unique method of maintaining 1 atm. If worse comes to worse, a microcontroller could work.
  .
• You can gear higher to decrease engine rpm's and switch out the cam to shift peak torque to lower rpms. Switching the cam allows lower rpms to be used and increases efficiency in that speed range (usually through early valve closing). The result is degraded top-end power, which can be overcome with complexity (VVT).
  .
• You can adjust the ECU to lean out the mixture. Leaning the mixture decreases the HP for a given throttle setting, which requires the butterfly valve to open more. Honda lean burn engine use this strategy to decrease pumping losses (as do diesels, I'm assuming).
  .
• You can increase EGR levels to achieve the same effect as lean burn, but you'll start to run into ignition issues. This can usually be overcome by "swirling" the mixture by leaving an intake valve closed and using a hotter spark plug.
  .
• You can use advanced variable valve timing/ignition control like BMW to totally remove the butterfly valve. Good luck, though...
  .
• You can downsize to a smaller engine that will be operate at its most efficient rpm when providing power for cruise. Acceleration can be handled by using a turbo to increase compression (w/ ethanol injection) and/or increasing volumetric efficiency >100% .
  .
• Depending on where you desire low-rpm efficiency, you can kill the engine and use an electric motor to tool about (hybrid technology). Easier conversions would include a lowerable "trolling" motor, upgraded starter for short hops, or a beefed up starter (i.e. belted starter/generator) for low speed movement.

If anyone has information beyond theory or different ideas feel free to post them. I don't know how else to go about the problem.

- LostCause