18 replies to this topic

[davidlan]

I don't know if this topic has arisen before but I had came across this concept

several years ago and then was surprised to see that some manufactures had decided

to pursue the concept.

 

http://thechronicleh...on-ratio-engine

 

Now while I understand the original idea I have to phrase the question. 'What is the point?'

We are now seeing the modern F1 engines achieving an almost 50% efficiency in conjunction

with batteries packs so why would this concept improve upon that.

 

Dav

 

 

[manolis]

Hello DavidIan

“What is the point?”

The point of a VCR is the engine to run at the best expansion ratio for the specific conditions of operation.

The F1 engines run most of the time at full load.

A conventional car engine runs, most of the time, at light or very light load wherein a higher expansion ratio would milk more energy from the fuel (higher thermal efficiency).
A medium size car makes some 200PS peak, however it needs less than 20PS to move at constant 100Km/h or 60mph on a level road.

Nissan’s VCR changes a lot the basic kinematic mechanism. The relative loads are different at low and high compression ratios. It adds bearings and friction.

With the pattakon VCR:



the basic kinematic mechanism doesn’t feel any change as the compression ratio varies. Either at low or at high compression ratios the pistons and the connecting rods move exactly the same way.

More at http://www.pattakon....pattakonVCR.htm



A more ambitious idea is to avoid the VCR by using unconventional valve trains allowing way higher compression ratios without knocking.

On 2003, the Bishop rotary valves prototype F1 engine was making some 10% more power than the conventional poppet valve F1 engines (more at http://home.people.n...AutoTechBRV.pdf ).

According Bishop:
“The numerous BRV engines tested over the last 18 years have all demonstrated remarkable resistance to engine knock. In the early 1990s engines with conventional bore/stroke ratios ran compression ratios as high as 15:1 on unleaded 93 octane pump petrol. The F1 single cylinder engine ran compression ratios as high as
17:1 using standard F1 fuels before settling on 15.3:1 as optimum. No evidence of knock has ever been observed . . . Testing of these engines was prematurely terminated when the FIA announced changes to Article 5.1.5
of the engine regulations late in 2004 with the specific purpose of banning this rotary valve technology.”


What if Nissan Infinity were using Bishop rotary valves:



or PatRoVa rotary valves:



(more at http://www.pattakon....akonPatRoVa.htm )

in its cylinder heads,
allowing the operation at 14:1 compression ratio at all conditions?

I.e. 14:1 expansion ratio at partial loads and 14:1 expansion ratio at full load (it is a turbocharged engine).

Thanks
Manolis Pattakos

[gruntguru]

Problem is F1 engines produce (more than) 50% efficiency but only in a narrow operating range (close to full power). Road cars spend most of their time at light load and the CR that avoids detonation at full load is way too load for best part load efficiency. The effect is even more pronounced with forced induction due to the greater dynamic range and of course forced induction + downsizing is becoming a popular technique for economy gains.

 

EDIT. Whoops. Manolis beat me to it.

 

Manolis. I think your rotary valve design would offer better combustion characteristics than the BRV. The combustion chamber is more compact, spark location more central, more squish. On the other hand the BRV has stronger tumble.

Edited by gruntguru, 06 October 2016 - 03:13.

[Speedman]

Hello Davidlan

 

 

What gruntguru says true.

 

Small note:

 

Formula 1 engines are turbo-compound engines and the efficiency is better than conventional F1 Turbo engines, but only of high load.

The efficiency of a turbo-compound engine is by low load is the same or more worse than a conventionell road car engine.

 

Turbo compound engines are even more extreme than conventional turbo engines (low load/ high load).

 

 

Best regards

Edited by Speedman, 06 October 2016 - 08:39.

[davidlan]

Thanks to all for your very informative responses an especially to Manolis.

 

While I am mechanically literate I am no engineer, but I do find advances like this immensely interesting.

All through while the explanation of the VCR is fairly easy to understand the Bishop Rotary Values lost me.

 

I do still have one question, what is the trigger to alter the compression chamber?

The process has to be related to the loads placed upon the engine so I am guessing it is all

software related.

 

Thanks

 

Dav 

[gruntguru]

Yes, all under control of the engine management computer.

[manolis]

Hello DavidIan.

You write:
“while the explanation of the VCR is fairly easy to understand the Bishop Rotary Values lost me”


In the tests, the engines with the Bishop rotary valve “demonstrated remarkable resistance to engine knock”. Even with 17:1 compression ratio “no evidence of knock has ever been observed”.

Compression ratios substantially higher than 15:1 are meaningless: the engine parts undergo heavier pressure loads, the mechanical friction increases, the exhaust emissions worsen, the fuel efficiency drops etc.

Even in the compression ignition engines (wherein there is no “knocking”) the “optimum” compression ratio used in cars is not high. In small Diesels a 14:1 compression ratio becomes common case. In the giant 2-stroke marine Diesels with the more than 50% BTE (Brake Thermal Efficiency), a 12:1, or even lower, compression ratio is the case.

So, an engine (turbocharged or not) capable to operate with the available fuel without knocking at a, say, 14:1 compression ratio, needs not a VCR.

The Nissan Infinity (as the rest poppet valve engines) cannot help knocking at heavy load and high compression ratio. This makes a VCR useful: at partial loads the engine runs on the high compression ratio (say 14:1), at heavy loads the compression ratio drops to avoid the knocking and the related problems.



From another viewpoint:

Suppose that tomorrow morning all car engines turn to Variable Compression Ratio engines, and that tomorrow afternoon a chemical engineer discovers / invents a harmless cheap “additive” that increases several time the knocking resistance of the existing fuels. The day after tomorrow all engines will return to non VCR engines.

Bishop’s rotary valve design was a kind of such “additive”.



You also write:
“I do still have one question, what is the trigger to alter the compression chamber? The process has to be related to the loads placed upon the engine so I am guessing it is all software related.”


The technology already exists. There are knock sensors in the car engines. They inform the ECU when the knocking starts (the most advanced knock sensors inform the ECU that the knocking is near to start) and the ECU aligns properly the spark advance etc.
In case of a VCR engine, the ECU “feels” when knocking happens (or, even better, when the knocking is close to start) and commands the VCR mechanism to lower the compression ratio.
When operating at stable conditions (say, for instance, in the highway at constant speed) the ECU could increase in small steps the compression ratio until to “feel” knocking. Then it lowers a little the compression ratio (for safety) and keeps in memory the data for future use.

Thanks
Manolis Pattakos

[gruntguru]

Compression ratios substantially higher than 15:1 are meaningless: the engine parts undergo heavier pressure loads, the mechanical friction increases, the exhaust emissions worsen, the fuel efficiency drops etc. . . . . .

 . . . . The Nissan Infinity (as the rest poppet valve engines) cannot help knocking at heavy load and high compression ratio. This makes a VCR useful: at partial loads the engine runs on the high compression ratio (say 14:1), at heavy loads the compression ratio drops to avoid the knocking and the related problems.

 

Mechanical compression ratios above 15:1 may be useful under part load conditions when peak pressures are much lower. This is particularly true for "high expansion ratio" cycles eg LIVC, Atkinson etc.

[Speedman]

Mechanical compression ratios above 15:1 may be useful under part load conditions when peak pressures are much lower. This is particularly true for "high expansion ratio" cycles eg LIVC, Atkinson etc.

 

That'sr right. Under part load is 19:1 oder perhaps more possibile.  HCCI is also a topic in the future.

Edited by Speedman, 08 October 2016 - 11:02.

[davidlan]

Manolis again thank you for such detailed and helpful information, but

I hate to say each time you answer It just creates other questions for me.

I took some time to review the information on the Bishop Rotary Valves and once I 

grasped the idea it of course led to yet more questions. The benefits of a bishop rotary Valve

in comparison to a standard poppet valve seem substantial yet other than Formula 1 no 

car manufacturers have seemed to pursued the concept.

1. Is this because the benefits only apply to a high performance engine as running a higher compression

would only shorter the life of a conventional engine?

2. Is the increased complexity of the Rotary valve simple a cost factor?

 

I apologize in advance, as I have stated before I am not a engineer but I do love knowledge.

 

Dav

[malbear]

The Beare head increases compression ratio if you ****** the upper piston as well as increasing the expansion ratio and opening the exhaust port late and closing the intake late . so advancing the upper piston decreases compression opens the exhaust early and shuts the intake earlier . so we have variable compression and valving with the one simple mechanism .

[davidlan]

Thank you Malbear I took a sweep around the net and found some very useful information and videos of the

6 stroke. 

Very clever 

 

Dav

[manolis]

Hello MalBeare.

Looking for “Bear-Head” in the Internet I found the http://www.sixstroke...vember_1994.pdf article.

I stopped reading it at the point wherein it writes:
“During the power stroke approximately 12% of the power is transmitted through the upper piston. The main piston losses about three per cent, therefore there is a net gain of nine per cent, all things being equal.”

What the “there is a net gain of nine per cent” means?

Thanks
Manolis Pattakos

[manolis]

Hello Dav.

You write:
“I hate to say each time you answer It just creates other questions for me. “

Do not stop making questions.



You also write:
“1. Is this because the benefits only apply to a high performance engine as running a higher compression would only shorter the life of a conventional engine?
2. Is the increased complexity of the Rotary valve simple a cost factor?”

Yes and no.

If the F1 rules were not changed to ban the rotary valves,

and if the Bishop rotary valve F1 engines were in practice (in the race) as good as in the lab,

the guys in Bishop could gather money, recognition and momentum to try to put their ideas in normal engines.

The change of the F1 rules killed instantly the Bishop project / company.


However, for normal applications the exhaust emissions of a mass production engine must comply with the regulations (like, say, Euro 6).

The specific lube consumption (grams of lubricant per kWh of energy produced) in a Bishop rotary valve engine cannot help being several times higher than in normal engines.
The BRV (Bishop Rotary Valve) needs lubricant for its seals, and it is difficult this lubricant to be collected and recycled because the seals pass over ports (as in the two strokes).
With plenty of lubricant into the combustion chamber the emissions worsen ( read at http://www.pattakon....ssionDiesel.pdf an article of MIT).


Coates uses dry seals in his Spherical Rotary Valves (CSRV) and “claims” he solved the problem.
However his patents already expired without achieving to put his spherical rotary valves in mass production, despite the millions invested, and lost, by his investors.



A simple rotary valve like the PatRoVa makes the cost of the cylinder head substantially lower. Reasonably, in mass production a PatRoVa cylinder head (there is only one moving part inside) of similar “capacity” with a Panigale Desmodromic cylinder head will have several times lower cost.

Thanks
Manolis Pattakos

[manolis]

Hello.

Too high compression ratios spoil the form of the combustion chamber .

With 400cc cylinder capacity:

8:1 compression ratio means a 57cc dead volume (the combustion chamber capacity when the piston is at TDC,

11:1 compression ratio means a 40cc dead volume (70% of the dead volume with 8:1 compression ratio),

14:1 compression ratio means a 31cc dead volume,

17:1 compression ratio means a 25cc dead volume (which is 62% of the dead volume with 11:1 compression ratio, and 44% of the dead volume with 8:1 compression ratio),

20:1 compression ratio means a 21cc dead volume.


On the other hand, suppose that “Bishop” tells the true and his rotary valve engine never knocked until, say, 17:1 compression ratio.
To add a VCR in order to go from the 17:1 to the, say, 20:1 compression ratios is meaningless. The improvement of the fuel efficiency at very light loads cannot justify the added complexity and cost.

Thanks
Manolis Pattakos

[davidlan]

So i can across a newer press release on the Infiniti VCR today, a little more detail

but still a little light on specifications.

Noticeable they are pointing out that the future  engine will include some form of Hybrid Tech but

are quoting compression rations of up to 18.1.

Thanks you again Manolis I really appreciate the time you must take in your responses and the truth be

told I am really enjoying educating myself.

 

David Landon 

[davidlan]

Ops it would help if I put the link in there.

 

http://www.msn.com/e...-BBwXumB#page=1

 

Dav

[gruntguru]

David, I second your appreciation. Manolis is a true innovator who has a sound grasp of the technical. Generally speaking one questions his assessments at one's peril.

[malbear]

manolis,

hello mate 

after two divorces a federal court case where the losing party did not pay me costs and a kid with cancer  and ASIC refusing to do its job because not wishing to denigrate a dying Ausy Icon , I will not pick up on an obscure point and engage in a mutual downward spiral of tit for tat  mutual denigration. jealousy can be a curse. I have admired and supported your work .