Go Back   EcoModder Forum > EcoModding > General Efficiency Discussion
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 12-05-2010, 11:48 PM   #141 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 12,762

Blue - '93 Ford Tempo
Last 3: 27.29 mpg (US)

F150 - '94 Ford F150 XLT 4x4
90 day: 18.5 mpg (US)

Sport Coupe - '92 Ford Tempo GL
Last 3: 69.62 mpg (US)

ShWing! - '82 honda gold wing Interstate
90 day: 33.65 mpg (US)

Moon Unit - '98 Mercury Sable LX Wagon
90 day: 21.24 mpg (US)
Thanks: 1,585
Thanked 3,552 Times in 2,216 Posts
Quote:
Originally Posted by todayican View Post
Potentially OT but thats a big part of my decision to go hybrid. use the E-motor for what its great at, low end torque and the diesel for what its good at, droning on for hours down the highway.
I don't know if there's a flaw in my thinking, but my idea of a hybrid would be opposite: ICE for acceleration (because 1: that is where the ICE is most efficient and 2: acceleration is a huge power draw vs cruising and fuel tanks carry far more power per pound than batteries) and electric for cruising, because cruise hp requirements are so much smaller than accel i.e. for a typical small car one might want 80 hp for accel but only need 10 hp to cruise.

That set-up is backwards from a vehicle range point of view, in that for long trips the batteries will likely get depleted before trip's end, whereas the other way probably only used a lil bit of battery at the beginning of the trip and one could simply keep fueling up along the way for infinite range. But I think with ICE accel/elec cruise overall trip efficiency would be maximized... No?

__________________


  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 12-06-2010, 12:01 AM   #142 (permalink)
Master EcoModder
 
Join Date: Apr 2010
Location: belgium, wi
Posts: 262

Bus - '94 Ford School Bus huge

Stupid - '01 Chevy Blazer LS
90 day: 21.38 mpg (US)

hawk - '00 Honda Superhawk
Thanks: 2
Thanked 24 Times in 19 Posts
it is hard to compare a subaru to other vehicles as all models post 1980's (could be wrong here with the date) are AWD. A lady friend of mine bought an impreza 5 speed recently and is getting between 28-31mpg. That isnt bad for all that extra spinning parts and weight.
  Reply With Quote
Old 12-06-2010, 12:05 AM   #143 (permalink)
MPGuino Supporter
 
t vago's Avatar
 
Join Date: Oct 2010
Location: Hungary
Posts: 1,769

iNXS - '10 Opel Zafira 111 Anniversary
Thanks: 802
Thanked 685 Times in 439 Posts
Regarding the Scuderi engine - I smell a scam. That engine supposedly compresses air using only one stage, to a pressure of 1885 psig or so. This compressed air can then supposedly go into a storage tank for re-use, or be directly injected into the combustion cylinder.

http://www.sae.org/mags/aei/POWER/7803

One problem with this idea is that this compressed air will reach a temperature of at least 1700 F, which will make any metal air cylinder glow cherry red after a while. Another problem I see is that this heated air will pretty much cause autoignition of any current fuel the moment it is injected into the airstream.
  Reply With Quote
Old 12-06-2010, 04:32 AM   #144 (permalink)
dcb
needs more cowbell
 
dcb's Avatar
 
Join Date: Feb 2008
Location: ˇ
Posts: 5,038

pimp mobile - '81 suzuki gs 250 t
90 day: 96.29 mpg (US)

schnitzel - '01 Volkswagen Golf TDI
90 day: 53.56 mpg (US)
Thanks: 158
Thanked 269 Times in 212 Posts
Quote:
Originally Posted by NeilBlanchard View Post
...
Keeping in mind that piston engines were invented for steam power, and adapted for gasoline -- steam has a (more or less) constant back pressure, so the pressure in the cylinder is maintained all the way to the bottom of the stroke. Whereas, ignited fuel in a much shorter expansion time, and since it start very near TDC, much of the peak pressure is "wasted" in bending the crankshaft sideways, rather than developing torque...
I don't understand entirely, you say the peak pressure at tdc is the issue, but that pressure doesn't go anywhere till the piston starts moving anyway, so what's the problem?!? Where did you see references to %50 efficiency improvements on cam based engines (and was it clear that it was a tdc based gain)?
__________________
WINDMILLS DO NOT WORK THAT WAY!!!
  Reply With Quote
Old 12-06-2010, 06:55 AM   #145 (permalink)
Master EcoModder
 
NeilBlanchard's Avatar
 
Join Date: May 2008
Location: Maynard, MA Eaarth
Posts: 7,901

Mica Blue - '05 Scion xA RS 2.0
Team Toyota
90 day: 42.48 mpg (US)

Forest - '15 Nissan Leaf S
Team Nissan
90 day: 156.46 mpg (US)

Number 7 - '15 VW e-Golf SEL
TEAM VW AUDI Group
90 day: 155.81 mpg (US)
Thanks: 3,466
Thanked 2,934 Times in 1,837 Posts
The peak pressure is bending the crankshaft sideways, rather than spinning it. It spends a relatively long time doing this. The connecting rod position relative to the crank center is one of the main reasons that current gasoline engines are so horribly innefficient -- 20-30 sucks, frankly.

And the pressure disputes as the volume expands. So by the time it has the maximum mechanical torque at 90 degrees past TDC, the pressure has dissipated a lot. In a steam engine, the pressure stays virtually constant all the way through the stroke.

The Revetec engine nearly doubles the efficiency of the bog standard design. So does the Atkinson cycle Prius engine.

The valve train is another major drain on efficiency -- it takes a lot to push open the typical poppet valves that require springs. Though, I don't know if there is an efficiency gain with a desmodromic valve train like Ducati's?

I am trying to get people to think unconventionally -- what we are doing can only be tweaked; when we need a quantum leap. Rotary engines (not necessarily Wankels) have an response to the crankshaft issue -- some of them at the very beginning of this thread look very promising.

My proposed design was an attempt to answer these problems without abandoning the crankshaft.
__________________
Sincerely, Neil

http://neilblanchard.blogspot.com/
  Reply With Quote
Old 12-06-2010, 08:00 AM   #146 (permalink)
Eco-ventor
 
jakobnev's Avatar
 
Join Date: Oct 2010
Location: sweden
Posts: 1,593

Princess - '92 Mazda MX-3 GS
House of Tudor
Team Mazda
90 day: 53.54 mpg (US)

Shirubāarō (*īω`*) - '05 Toyota Prius Executive
Team Toyota
90 day: 54.88 mpg (US)

Blue Thunder - '20 Hyundai IONIQ Trend PHEV
Team Hyundai
Plug-in Hybrids
90 day: 208.47 mpg (US)
Thanks: 72
Thanked 673 Times in 424 Posts
Send a message via MSN to jakobnev
Quote:
Originally Posted by Frank Lee View Post
I have a suspicion that eliminating the throttle plate won't cut pumping losses, if it's done by manipulating valve timing, cuz then the restriction that the piston sees on the downward stroke would be caused by the intake valve. However if Toyota is doing something else then good.
I'll try to illustrate the difference with a couple of idealized graphs.

valvetime.png shows piston position on the x-axis and cylinder pressure on the y-axis. the green line shown cylinder pressure in an engine that uses no throttle, and instead only has the intake valve open until the needed charge had been drawn in. The red line shows cylinder pressure in a conventional throttled engine. The mild green area illustrates the energy saved on each intake stroke.

pushout.png illustrates the effect of having a less restrictive throttle and keeping the intake valve open "too long" after BDC. The red line is again a conventional engine and the mild green area represents the energy saved on each intake stroke.

Minor oops: the area marked after BDC shouldn't be green, it should be brown or something instead, since it doesn't represent energy saved. (but rather the opposite)
Attached Thumbnails
Click image for larger version

Name:	valvetime.png
Views:	17
Size:	1.4 KB
ID:	7480   Click image for larger version

Name:	pushout.png
Views:	12
Size:	2.1 KB
ID:	7481  

Last edited by jakobnev; 12-06-2010 at 08:11 AM..
  Reply With Quote
Old 12-06-2010, 08:18 AM   #147 (permalink)
MPGuino Supporter
 
t vago's Avatar
 
Join Date: Oct 2010
Location: Hungary
Posts: 1,769

iNXS - '10 Opel Zafira 111 Anniversary
Thanks: 802
Thanked 685 Times in 439 Posts
Quote:
Originally Posted by NeilBlanchard View Post
The peak pressure is bending the crankshaft sideways, rather than spinning it. It spends a relatively long time doing this. The connecting rod position relative to the crank center is one of the main reasons that current gasoline engines are so horribly innefficient -- 20-30 sucks, frankly.

And the pressure disputes as the volume expands. So by the time it has the maximum mechanical torque at 90 degrees past TDC, the pressure has dissipated a lot. In a steam engine, the pressure stays virtually constant all the way through the stroke.
There's a reason why we don't use constant pressure processes to extract work. Say you have a cylinder arrangement of some starting volume v1, and some ending volume v2 which is some multiple of v1. (incidentally, that's called the compression ratio). Work is extracted from this cylinder arrangement, and can be calculated.

Now, we have to model two cases here. The first case is of this so-called inefficient process of allowing a maximum pressure at v1, and allowing that pressure to fall as v1 expands to become v2. The second process is the other process of allowing pressure to remain constant while v1 expands to become v2, as in the steam piston.

The first process is called an adiabatic, or constant heat energy process (since no heat energy is being added or subtracted here). Remember that the first process assumed a maximum pressure at v1. For a real gasoline engine where pressure builds up as the combustion inside the cylinder proceeds to completion, and as a little heat energy actually leaves in the form of waste heat into the cylinder walls, this is an approximation, but is fine for our purposes of illustration.

The second process is called an isobaric, or constant pressure process. Note that heat energy is continually added in the form of more steam, in order to keep the pressure constant inside the cylinder. Again, there will be a little heat lost to the cylinder walls, but this can also be ignored for now.

The reason I ignore the real-world heat energy loss and internal combustion pressure increase behavior is that it can be assumed that the process happens quickly enough so that heat energy loss can be assumed to be zero. Similarly, the combustion and resultant pressure increase can be assumed to be instantaneous, since we are talking about a time span of milliseconds here.

Given that, we can set up a couple of thermodynamic equations and solve for the amount of useful work that will be extracted in either case. I will not bore you with the equations in this particular post, since a lot of boredom already was generated in the above paragraphs (but will be more than happy to post the equations here, if asked).

It turns out that you can extract some quantity of useful work w, given the adiabatic process. Now, and this is the important part here - you can extract about 0.23 w from the isobaric process. That's less than 1/4 of the work that was extracted from the adiabatic process.

Even if you divide the work output of the adiabatic process by 2, to simulate the 4-stroke nature of an internal combustion engine, you end up having a process that is still more than twice as efficient at extracting useful work than a steam engine cylinder.

Quote:
Originally Posted by NeilBlanchard View Post
The Revetec engine nearly doubles the efficiency of the bog standard design. So does the Atkinson cycle Prius engine.
This is misleading. The Revetec engine is still a dream, as is this other Scuderi engine I looked at last night. You would think that it would be possible for them to have provided something by now, if this engine were as efficient as is claimed. Scuderi has had 9 years to develop their engine. Revetec has had even longer (15 years). Surely, if nothing else, a small engine based on either design could have been made available to the general public by now, if for nothing more than for powering lawn mowers or similar.

As for the Prius engine? It has to do a job that is different from a normal IC engine. You've noticed that the engine is more efficient? You will also notice that power and torque are reduced in the Prius engine, compared to an otherwise equivalent gasoline engine, and that's so that the Prius engine can more effectively drive an electric propulsion system. Also, the Prius engine has no parasitic loads it has to drive (unlike a standard gasoline engine).

In order to make a gasoline engine more efficient, you're going to have to sacrifice some power and torque somewhere. That's the nature of the beast.

Quote:
Originally Posted by NeilBlanchard View Post
The valve train is another major drain on efficiency -- it takes a lot to push open the typical poppet valves that require springs. Though, I don't know if there is an efficiency gain with a desmodromic valve train like Ducati's?
The beauty of springs are that you get that energy back when the springs expand. The real losses in a valvetrain are due to frictional losses, not springs. Besides, you're talking about a loss of perhaps 1 HP, if that. Reduce the friction losses in a valvetrain by 25%, and you'd be lucky to see a 1% increase in fuel economy.

Quote:
Originally Posted by NeilBlanchard View Post
I am trying to get people to think unconventionally -- what we are doing can only be tweaked; when we need a quantum leap. Rotary engines (not necessarily Wankels) have an response to the crankshaft issue -- some of them at the very beginning of this thread look very promising.

My proposed design was an attempt to answer these problems without abandoning the crankshaft.
You are going to run up against engineering realities, even with thinking unconventionally. It's nice to have a pretty idea for a new-wave engine process, but it will have to run against the real world with all of its limitations. Materials engineering, and pesky real-world behavior that refuses to agree perfectly with ideal conditions, result in what you see today.
  Reply With Quote
The Following 3 Users Say Thank You to t vago For This Useful Post:
NeilBlanchard (12-06-2010), some_other_dave (12-06-2010), UFO (12-06-2010)
Old 12-06-2010, 08:27 AM   #148 (permalink)
MPGuino Supporter
 
t vago's Avatar
 
Join Date: Oct 2010
Location: Hungary
Posts: 1,769

iNXS - '10 Opel Zafira 111 Anniversary
Thanks: 802
Thanked 685 Times in 439 Posts
Quote:
Originally Posted by jakobnev View Post
I'll try to illustrate the difference with a couple of idealized graphs.
This is the idea that drives concepts like displacement on demand, valve throttling, and (to a lesser extent) variable valve timing. This is the idea that illustrates why a diesel engine is generally more efficient than an otherwise equivalent gasoline engine. The higher compression ratio of a diesel engine does not provide as much fuel economy savings as is generally thought.

It takes energy to generate a vacuum inside the intake manifold, and it takes even more energy to suck air past that hideously restrictive throttle plate. Those two energy draws are interrelated, but are in fact separate. That's in addition to having to suck air past the poppet valves in the head. Keep in mind that these energy draws are not used in generating any useful output.

It is still possible to generate an intake vacuum without using a throttle plate to restrict air. If you use a small enough venturi, you can allow the sonic speed of the incoming airflow to limit the airflow itself to act as an effective throttle, and the venturi will allow that self-limited airflow to expand to form the vacuum.

Last edited by t vago; 12-06-2010 at 08:44 AM..
  Reply With Quote
Old 12-06-2010, 09:40 AM   #149 (permalink)
Master EcoModder
 
Join Date: Sep 2009
Posts: 5,927
Thanks: 877
Thanked 2,023 Times in 1,304 Posts
t vago

what do you think of the rotary engine design in the linked utube video? I understand it is operating as an air driven pump in the video, but I would be interested in your opinion.

I thought the greater efficiency in a diesel was due to the higher energy content of the fuel. Measured by the energy content of the fuel alone the diesels efficiency would be more comparable to a spark ignition gasoline engine.

Also what is you opinion of the Transonic type of super critical fuel injection?

regards
Mech
  Reply With Quote
Old 12-06-2010, 10:07 AM   #150 (permalink)
dcb
needs more cowbell
 
dcb's Avatar
 
Join Date: Feb 2008
Location: ˇ
Posts: 5,038

pimp mobile - '81 suzuki gs 250 t
90 day: 96.29 mpg (US)

schnitzel - '01 Volkswagen Golf TDI
90 day: 53.56 mpg (US)
Thanks: 158
Thanked 269 Times in 212 Posts
diesels are also throttle-free, and have high compression ratios, and direct injection these days, those help too.

__________________
WINDMILLS DO NOT WORK THAT WAY!!!
  Reply With Quote
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Discussion on tire efficiency Ernie Rogers General Efficiency Discussion 69 12-27-2014 01:17 PM
The Easy Leg: Vehicle Efficiency natefish Off-Topic Tech 17 05-19-2010 04:52 PM
Vehicle Efficiency Improvements SVOboy EcoModder Blog Discussion 24 12-07-2009 10:19 PM
Worldís cleanest internal combustion engines? blueflame EcoModding Central 6 02-28-2009 08:13 PM
Low-Drag Trucks: Aerodynamic Improvements & Flow Control System Boost Fuel Efficiency OokiiMamoru Aerodynamics 5 06-15-2008 11:38 PM



Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2022, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com