BMW's throttle-less engines
BMW's throttle-less engines
(OP)
Why does it get bandied about that these engines don't have pumping losses? As far as I'm concerned a restriction is a restriction. The only advantage in terms of pumping loss I can imagine is a possible reduction in turbulence of the incoming charge which at part-load might not be an advantage at all because of charge mixing.





RE: BMW's throttle-less engines
RE: BMW's throttle-less engines
I don't really know if that's how BMW does it, but that's what popped into my head when thinking about it.
RE: BMW's throttle-less engines
RE: BMW's throttle-less engines
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RE: BMW's throttle-less engines
schmidtj86 (Mechanical) said:
Also if you close the intake very early, there is no pumping losses when the piston goes down, because that same force that resists it going down, helps it come up (neglecting heat transfer, and friction).
Crystalclear:
Okay. But that's not what they are doing, is it? They are not closing it earlier if they want to partially fill a cylinder, they are closing it later. Normally you are sucking air past a restriction to run at low load. If you want to half fill a cylinder with air you could create a (throttle) restriction in the air flow, causing a pressure drop, and completely fill a cylinder with air at 1/2 an atmosphere pressure. Alternatively, you could close the intake valve when the piston was half way up and have half a cylinder of air at normal atmospheric pressure.
Now let's forget about the cylinder in both cases, as somebody will argue that (in the throttled case) the partial vacuum will help suck the piston up at the start of the compression stoke. But the work done to create a partial vacuum between the throttle and intake valve is lost.
Pumping losses is a generic term. You have to (1) suck air past a throttle. You have to (2) suck air past an intake valve and exhaust gas energy or a piston has to (3) push air past an exhaust valve.
Intake valve throttling is about reducing (1) the losses sucking air past the throttle, particularly at part load, by not having the throttle. I don't see how intake valve throttling can fail to recover the energy cost of creating the partical vaccuum between throttle and intake valve: energy lost when the intake valve closes and air seeps past the partially operated throttle ready to fill the cylinder when the intake valve opens next time.
RE: BMW's throttle-less engines
RE: BMW's throttle-less engines
RE: BMW's throttle-less engines
http:
has some figures for PMEPs on the last page, showing what is possible eliminating the throttle and controlling the valves. Unfortunately they show dual variable cam phasing (rather than intake only) and don't show the base figures for comparison.
From Mitsubishi Motors Technical Review 2005 No. 17.
http://w
MMC’s GDI technology was hailed
inside and outside Japan as the ultimate means of overcoming
the inherent shortcomings of gasoline engines.
The higher thermal efficiency yielded by GDI technology
prompted some observers to comment that there
was no longer any need for passenger-car diesel
engines; it triggered the subsequent advance from indirect-
injection diesel engines (the type of engine that had
been prevalent in diesel passenger cars) to direct-injection
diesel engines. Diesel engines have since shown
great advances in power, thermal efficiency, and emissions
performance owing to high-pressure direct injection
(made possible by electronically controlled common-
rail fuel-injection technology) and to high boost
pressure (made possible by advanced turbochargers).
In fact, the most important advantage of gasoline
engines, namely the ease with which load control can
be effected using throttle valves, has come to be seen
as less of an advantage since the pumping losses
caused by throttle valves are hindering improvements
in gasoline engines’ thermal efficiency. To remedy this
situation, it is urgently important to eliminate the factor
that is hindering improvements in gasoline engines’
thermal efficiency. In other words, gasoline-engine
developers are likely to pursue higher thermal efficien-
cy using throttle-valve-less designs while seeking further
improvements in gasoline engines’ inherently high
power density.
(My highlighting.)
RE: BMW's throttle-less engines
My conclusion was its a great thing in a laboratory but isn't practical in mainstream cars. 1st its dificult to have all valve events the same at all operating conditions.
Secondly IVT is great for light load but it imposes lots of detonation problems at heavy load because you can't get rid of the fast burn.
After 10 years and 500 thousand dollars of research I concluded the best implementation of variable valve timing was via patent 4,961,406.
In my opinion the engine of the future is basically using an early close atkinson cycle at heavy load and a late close atkinson cycle at light load.
The big advantage of the early close atkinson engine at heavy load is it has a cooler intake charge which alows a higher bmep without incurring detonation.
The cost to implement this control strategy is minimal considering most new engines have VVT technology
RE: BMW's throttle-less engines
RE: BMW's throttle-less engines
RE: BMW's throttle-less engines
RE: BMW's throttle-less engines
The 2007 Camry hybrid again has an atkinson cycle engine:
http://www
Also I don't see why lean mixture and atkinson cycle can't be combined.
Once they start to introduce electric superchargers such as these: htt
RE: BMW's throttle-less engines
Restricting performance via valve timing rather than throttling is even better.
For the doubters, short of running an engine with czyl pressure tapping, simply utilise a simulation package such as GT power or Ricardo Wave and do a comparison