underdriven Roots blower for throttling loss reduction

[Christ]

Nobody's ever done the solenoid controlled valve system yet (that I'm aware of), but with or without boost, it completely negates the need for any type of throttle restriction. That along with it's many other potential benefits, I'd be looking into something like that, long before attempting to use unnecessary addition of parts, drag, expense, as well as extra weight and increased load to justify removing a simple plate or the functionality thereof.

Just me, though. Proceed, sirs.

[Frank Lee]

I really like the concept and have thought of it much a long time ago. I got hung up on having nice, responsive controllability of it and concluded it would really have the most merit on stationary engines or engines that don't see such a wide range of throttling and rpm conditions, maybe tractors, mowers, generators, etc. but then of course there is the complexity and expense. Could be wrong about that though!

[serialk11r]

The initial benefit I saw was that you could use a CVT or electric motor to drive the supercharger and then be able to control engine output in a very simple and possibly responsive way. However having an electric motor controlling it is going to be complicated anyways, and a CVT probably doesn't change ratios quickly enough to have any sort of acceptable response.

The most efficient way to try to get energy back from the intake would be with an actual turbine, not a compressor run backwards, but at ~70% max efficiency + friction losses + varying performance across rev range it's hard to justify the cost.

[jakobnev]

The most efficient way to try to get energy back from the intake would be with an actual turbine

http://ecomodder.com/forum/showthrea...tem-19845.html

It even used exhaust heat and an intercooler to have the gasses at an elevated temperature when going through the turbine.

[Christ]

Originally Posted by serialk11r

The initial benefit I saw was that you could use a CVT or electric motor to drive the supercharger and then be able to control engine output in a very simple and possibly responsive way. However having an electric motor controlling it is going to be complicated anyways, and a CVT probably doesn't change ratios quickly enough to have any sort of acceptable response.

The most efficient way to try to get energy back from the intake would be with an actual turbine, not a compressor run backwards, but at ~70% max efficiency + friction losses + varying performance across rev range it's hard to justify the cost.

CVT is already a ~20ish % loss in energy to friction losses in most cases.

If I gather what you're saying correctly, you intend to replace the throttle plate with what amounts to a variable restriction that generates torque based on air flow through the intake under vacuum?

If that's the case, abandon hope all ye who enter here. If I remember correctly, the most energy that can be theoretically extracted from any source which requires fluid movement (i.e. wind) is less than 50% of the overall energy. Wind turbines, for example, would not be able to harvest more than 50% of the energy of the wind, because doing so would necessitate the wind to literally stop at the turbine face, returning zero energy for all it's effort.

So now that you're taking about 50% of the energy of a vacuum (oh, no), and putting it through CVT, you're looking at a (conservatively) 15% loss, leaving you with 85% of the original 50%, leaving you with 42.5%.

Let's say your vacuum under full load is sufficient to provide 10 lbft of torque via air movement - you can now only extract a maximum of 5, and after the loss, redeliver 4.25 to the crankshaft, all things theoretically at their best values.

Reconsider, however, that you're technically introducing a new restriction to the intake, increasing the vacuum and, by relation, the subsequent load on the engine, causing more "work" to extract the "Work" that you intended to redeliver to the crank.

If that's not what you were alluding to, please explain further.

[Christ]

Originally Posted by Frank Lee

I really like the concept and have thought of it much a long time ago. I got hung up on having nice, responsive controllability of it and concluded it would really have the most merit on stationary engines or engines that don't see such a wide range of throttling and rpm conditions, maybe tractors, mowers, generators, etc. but then of course there is the complexity and expense. Could be wrong about that though!

With the advent of computer controls and ever faster response times in said controls, I think it's something that could be a reality today.

Using all the same sensors currently in use, possibly a few more, to define the "curves" necessary for each solenoid's map set.

The first thing I'd ever bother trying it out on would be a single cylinder briggs or something, though, because the designs are transcendent and if it works on a single cylinder, it shouldn't be /too/ hard to adapt to more, if we're to treat each cylinder of an engine like it should be, as an individual engine, independent of the other cylinders.

[smokey442]

How about no throttle restriction and just randomly pulse injectors to provide fuel for a given power demand. Like the old hit and miss engines of the early 1900's ?

[Christ]

Originally Posted by smokey442

How about no throttle restriction and just randomly pulse injectors to provide fuel for a given power demand. Like the old hit and miss engines of the early 1900's ?

Someone tried that here, using a variable control for the injector pulse instead of a throttle control. The car was a Honda DelSol, I can't remember the username of the character involved in the project, though.

He ended up making a millisecond long mistake and burning a piston crown, IIRC.

However, with controls that would prevent one from over-leaning/overloading at the same time, this is, in fact, a viable option, at least so far as was proven by the experiment.

[hawk2100n]

Originally Posted by serialk11r

The initial benefit I saw was that you could use a CVT or electric motor to drive the supercharger and then be able to control engine output in a very simple and possibly responsive way. However having an electric motor controlling it is going to be complicated anyways, and a CVT probably doesn't change ratios quickly enough to have any sort of acceptable response.

The most efficient way to try to get energy back from the intake would be with an actual turbine, not a compressor run backwards, but at ~70% max efficiency + friction losses + varying performance across rev range it's hard to justify the cost.

I apologize to continue to shoot your ideas down but extracting work from the incoming air is different than throttling losses.

Newtonian physics states that work is the product of force and distance. In this case the force is the pressure over the area of the rotor that is being acted upon and the distance is that portion of the rotation, dTheta. In order for work to be extracted from the system you must have a dThetha that is non-zero. You get an easily quantifiable amount of work being performed. Now on a throttle body you have some area but it isn't being moved so there is no work being performed.

Since the piston drawing air into the system is the source of the energy and is creating the potential energy in the form of a pressure differential, it MUST be doing work on the rotor. However it is not doing work on the throttle body because the throttle body does not move. Therefore, for work to be extracted from the blower, it must be extracting work that would otherwise not be extracted from the system.

[serialk11r]

I already shot my own idea down, the only energy recoverable is miniscule in most cases due to the way Roots blowers are built.

I know no work is performed on the throttle body, the point is that there is an energy loss due to free expansion at the throttle body in the typical case. Cylinders drawing air unevenly reduces this slightly. As I wrote, a Roots blower would suffer nearly the same magnitude of loss to free expansion while having additional inefficiencies, thus it's not a good idea. I was mistaken in thinking it would recover significant energy because that energy would come from the pistons pulling a deeper vacuum.

And again, if the Roots blower exit was coupled more or less directly to the intake valves then it would be a different story but that's very difficult to do.