Reducing throttling losses?
 

I've in the past maintained that, for gasoline engines, intake losses are composed of pumping losses, of which intake manifold vacuum is the result; and throttling losses, which is the energy required to suck air past a very inefficient blockage. Most people have either implied or concluded that throttling losses are negligible compared to pumping losses. Others lump throttling losses right into pumping losses, and with reason: The throttle itself helps to cause intake manifold vacuum, right? How would one go about separating the two effects if they're intertwined? I've even lumped this in, on other threads of mine, so as to simplify explanations.

Well, now I'm going to ask: What if throttling losses are significant? What if they can be lowered? And I'm going to refer to these quick Paint drawings:

http://www.tom-viki.com/spgm/gal/Car...rottle0002.png

Here is a simplified representation of my throttle body. Causing air to be sucked past the two circled little openings at either end of the throttle plate will take a lot of energy. This energy is taken from the mechanical energy that the engine just got done developing. Since the openings are so small, the incoming air is going to be accelerated a great deal while inside the small openings. This airflow will have a high average velocity, and that will translate into a lot of turbulence immediately past the throttle plate.

Note the interesting little curve at the bottom, where the lower throttle plate edge is at. I suspect that Dodge put that there in order to aid in driveability, and to reduce throttling losses at slightly-open throttle conditions.

Now, to my proposal: Put a wedge on the lower throttle plate, like this:

http://www.tom-viki.com/spgm/gal/Car...rottle0004.png

Note that effectively, we've gone from two small openings to one small opening. The wedge blocks the lower throttle plate opening. Obviously, to get as much air into the engine as before, we would have to... open the throttle. Which leads to picture 3:

http://www.tom-viki.com/spgm/gal/Car...rottle0006.png

Note that the upper opening has widened a bit, and that the lower opening remains closed. There should be a bit less turbulence just past the throttle plate, since the wider top opening should allow the incoming air to have a lower average velocity, which will lessen the turbulence behind the throttle plate.

I am going to be testing this idea. I found a throttle plate with a wedge from a junked Volvo 850, and it happens to have the exact same minimum and maximum diameters as the throttle plate in my truck's throttle body. I've already adapted the Volvo plate to my truck's throttle body, and have taken the truck on an initial test run composed of about 85% city driving. Results are promising.

i always suspected it was for a more progressive throttle opening

CV carbs.

Controllable intake valve throttling.

There, now you have the simple solution and the not-so-simple-but-much-more-effective-and-elegant-solution.

Back in the stone age I read BMW was playing with throttle-via-intake valve. I wonder what ever came of it...

Lots of paperwork and time/expense.

They still use it. Problem is it's complicated and noisy and a bee-yotch to maintain, supposedly. There's still a throttle plate, just in case the system fails and defaults back to normal valve operation.

-

Always wondered if you could do throttle-less more cheaply... like say, using an intake tube that's flexible, and having bladders control tube diameter... :p

Valvetronic - Wikipedia, the free encyclopedia

Requires a vacuum pump, because there is no manifold vacuum. It has a throttle plate for startup (that goes wide open once the valvetronic takes over) and emergencies (in case the valvetronic craps out).

If my interpretation of my limited reading is correct, a similar system (to Valvetronic) is used on the MINIs.

The wedge throttle sounds intriguing. The idea could be extended further, so that there is only one gap for air to go through at all times, instead of just at very low throttle openings. The slide valves used in some race cars would be one way to do that--the throttle plate slides out of the way instead of rotating out of the way. The intent in a race car, of course, was to eliminate the restriction from the open throttle plate, but it would give you only the one opening.

Perhaps an iris? That would be quite mechanically complex though.

Neat ideas to play with.

I look forward to seeing the results of your testing!

-soD

Unofficial first results:
2.76 gallons consumed over 59.3 miles -> 21.5 MPG average
90 degrees F outside/140 degrees intake air temp
A/C on
average speed 64 MPH

Now, some problems I've noted:

Going straight and level produced most of the MPG gains. Compared to my previous throttle, though, MPG suffered more when going up inclines. For instance, there's a stretch of road about a mile long that is about a 2% incline. With the old throttle, I could expect to see an instantaneous MPG reading of about 18 MPG on the overhead display, corrected to about 16 MPG actual. With the wedge in place, I saw 15 MPG on the overhead display, corrected to 13.5 MPG actual.

I will have hard numbers tonight, on my homebound commute.

CV carbs still use a throttle plate.

As was pointed out, that's kind of complicated and expensive. Especially if the vehicle in question never came with this feature from the factory. It's a really nice idea, though.

That would be nice. You could reduce turbulence to almost nothing. Not sure how long the materials would last, though.

That sounds kind of like a barrel throttle. I understand they're used in performance motocross.

Hm... This was something I also considered

An iris throttle might could work, too. Certainly better than a butterfly valve. But, yah, it'd be a mechanical nightmare.

I always liked the idea of getting some energy out of anything that costs you energy. I guess it comes from the old vacuum operated wipers. Not that they were that good but they used some of the energy lost in a throttle restriction.

I think of it as a column of air extending into outer space that is trying to crush everything on the planet. It's astounding how much total pressure is exerted on our skin surface at 14.7 pounds per square inch.

regards
Mech

I've been giving throttling some thought, and came up with this idea:

http://www.tom-viki.com/spgm/gal/Car...rithrottle.png

The idea is to have a venturi with a convergent and a divergent nozzle. There'd be a teardrop shape that would move into and out of the venturi throat, which would accomplish the necessary throttling. Ideally, there'd be no turbulence at all.

No matter what method you use your still going to have throttle losses when creating a vacume. Cylinder deactivation has been around for awhile and has been documented in that reduces fuel consumption at part throttle operation. I think removing the throttle restriction compleatly and injecting fuel on as needed basis for less then full power needs would achieve this. Think of the hit and miss engines of days gone by.

I also agree that you are barking up the wrong tree. The drag that is costing energy is created at the piston top. There have been some good ideas bantered like cylinder deactivation, some not mentioned but discussed before like reducing RPM through gearing, introducing inert material to create additional pressure (EGR or water) or running lean.

You can get a similar effect to what you seek by advancing your intake lobe on the cam but this is only good if your CR is not already relatively high (as you are moving the opposite of Atkinson effect). I think a smaller intake plenum would also have a similar effect.

I didn't mean CV, I meant the ones that have a direct action sliding throat valve, like older Honda quads.

You're describing pumping loss. And, yes, vacuum creation will always be associated with pumping loss.

What I'm trying to describe is this:

http://www.tom-viki.com/spgm/gal/Car...turbulence.jpg

Note the circled part, which shows nice, pretty eddy currents right behind the partly opened throttle plate. That happens because a vacuum is being generated, and is in addition to pumping loss. The stuff that I've circled is what I'm trying to minimize.

Sure. All of these will reduce pumping loss, and will likely reduce throttling loss as well. However, I am primarily focusing on reducing throttling loss right at the throttle body.

What would that do for exhaust? I can't advance the intake lobes by themselves. The truck engine is a SOHC design.

That's not really possible without spending hundreds (or thousands) of dollars into having a custom, one-off intake manifold fabricated. All sorts of things have to be taken into consideration: airflow into the individual runners, interaction between cylinders, effects of different engine speeds on airflow.... Not something I want to focus on, right now.

Something like this?

http://www.myronsmopeds.com/wp-conte...d-744x1024.jpg

I guess I wasn't clear but I am in the camp that throttle losses are irrelevant for a fuel economy problem. As long as we are dealing with a part throttle condition its not an airflow problem. The engine doesn't feel drag from the pressure drop at the throttle, the engine feels drag from the vacuum at the piston tops. As long as we are in the part throttle region the engine only cares that it sees the % of cylinder filling it needs to meet the torque demands at that steady state condition.

To illustrate my earlier point, imagine that all of the cylinder filling occurs during only one degree of the 180 degrees of the intake stroke. Would you rather have all that filling at the start so the vacuum is near zero (or more likely positive pressure, but lets assume zero vacuum for multiple degrees) at the start and slowly increases for the length or the stroke OR a perfect vacuum for 179 degrees and full filling at the end. There may be minuscule gains fiddling with throttle shapes and port configurations but if you are truly chasing the elimination of this loss the real way to do it is advance the intake lobe on the cam.

You would have to experiment or gets some advanced engine software, you would have to think the original engineers did a fairly decent job to start with. You could buy a after market cam with a wider lobe separation angle or LDA.

You can epoxy the manifold for peanuts but again, you may dump a huge amount of high RPM flow for tiny gains on the low end. Again the original engineers probably have your engine dialed in pretty well already.

Label	Date/Time	Distance	Consumed	FE	OAT	IAT	delta-T	Status
B	16-Jun-2012 1:32 AM	58.7 miles	2.89 gallons	20.31 MPG	67 F	118 F	51 F	Active
B	19-Jun-2012 1:32 AM	58.7 miles	2.93 gallons	20.03 MPG	68 F	119 F	51 F	Active

I consumed 1.4% more fuel today, than on Friday. In other words, no significant change in fuel economy over the course of my homeward commute.

I'm still investigating this idea further. The increase in fuel economy during straight and level stretches of road (and downhill inclines) are offset by a decrease in fuel economy on uphill inclines. I have observed fuel economy in-town of around 21 MPG with the wedge, which is slightly more than the 18 MPG I had been getting without the wedge, and slightly higher than the EPA rating of 13 MPG.

Ugh... Guess I must check my tire pressures more often. Right rear was at 15 psig - not so good.

Well, today I could do more than just pump air into the tire, like I had been doing the past two days. Swapped the leaky tire with the spare, and will take the leaky tire to Sam's Club tomorrow to get it repaired. The leaky tire has a nice, pretty nail embedded into the tread. All 4 tires are again at 44 psig and steady.

I will have a good data set tonight, hopefully, that I can compare to the 16 June readings above.

Label	Date/Time	Distance	Consumed	FE	OAT	IAT	delta-T	Status
B	16-Jun-2012 1:32 AM	58.7 miles	2.89 gallons	20.31 MPG	67 F	118 F	51 F	Active
B	22-Jun-2012 1:47 AM	58.7 miles	2.77 gallons	21.19 MPG	72 F	122 F	50 F	Active

Amazing what fully inflated tires can do... The throttle body wedge provided a 4.1% improvement in fuel economy.

I think there is some merit in pursuing this idea further, of reducing throttling loss.

why not dome the rod side of the throttle plate(or the inverse); to ease the transitional flow.