Diesel Engine valve overlap period

To allow the incoming air to help purge out the exhaust remaining in the cylinder.

And, along the same lines, to allow the inertia of the exhaust in the exhaust pipe to help lower the pressure in the cylinder, helping to scavenge it. If it were not for these effects, the intake stroke would start with the combustion chamber (about 1/20 of the swept volume in a diesel) full of exhaust.

thanks Blink.

That's not true of a Carbon Ceramic Sealed, Spherical Rotary-Valve, Diesel Engine.

www.coatesengine.com

Although the website gives nearly zero technical information (and the voice-over is blatantly misleading when it compares the Coates engine to "its predecessor, the internal combustion engine"), I see nothing whatsoever that reduces or eliminates the valve overlap - in fact, based upon geometrical considerations, it may well be greater, as the cams cannot rotate beyond half crankshaft speed, while various techniques (roller cams, rocker arms, e.g.) can increase the instantaneous acceleration / deceleration of conventional valves at the opening or closing points in their operation. This takes nothing away from the Coates engine system, but why do you say that the statement is untrue for it? Is there a different purpose for overlap there?

Rotary valves have been around for a long time in various forms, though this is the first I've seen that solves the lubrication issues. All the others used overlap for the identical reasons that poppets do: to take advantage of charge momentum and scavenging. Even one using a rotating tube with angled baffles inside (so that a single port in the chamber was both intake & exhaust as the openings on the opposite side of the tube aligned with intake & exhaust manifolds alternately) had overlap. So did solenoid-actuated valves on a camless engine.

I'd agree that the video is very misleading and deceptive. The shot of the engine ostensibly running and shaking on a roll-around engine stand with Dad wearing hearing protectors, the open headers apparently exhausting into the room is completely absurd... as is the shot of the display valve train being motored over at a fraction of running speed with a rag used to show how clean the valve spheres are!

This is from a press release:

You see, in the last 60's and 70's most vehicles combustion engines in the U.S. were running at a compression rate of 12 to 1, which resulted in engine efficiency of about 35 percent. The rest of the engine power was lost in friction, pumping and heat loss. When it was found that lead additives in fuel had an adverse effect on the environment, the lead was removed from the fuel. However, this caused the poppet valves and combustion chamber on the poppet valve engines to overheat, raising the temperature to in excess of 2500 degrees and damaging the poppet values.

The answer was to lower the compression ratio of all engines to 10 to 1 or lower, thus reducing efficiency of the combustion engine to approximately 24 percent.

Almost every statement made in the release is wrong. In the 60's and 70's, most engines did not run at 12:1 compression ratios (the 1961 VW for example was 7:1, and mid 60's corvettes were 10.5:1 or 11:1). Efficiency was not 35%. The lack of lead did not cause overheating. (The lead acted as a valve seat lubricant, so harder valve seats were used in lead-free engines.) Lowering compression ratios "to 10 to 1 or lower" was not "the answer" to poppet "value" damage.

The Coates valve system might have some benefits, but the video and website material does nothing to support such a contention, and does much to erode confidence in the system -- it comes across as a scam, whether it is or not, because there are so many misstatements of fact. There is absolutely nothing presented that would indicate how rotary valves would reduce emissions, nor is there anything that clearly supports the contention that keeping oil out of the head area (how are the valve shaft journals lubricated?) would cause oil change intervals to go from 3000 miles to 50,000 miles. The underside of pistons, routinely oil cooled, are certainly as hot as the water cooled head on most engines, so peak oil temperatures cannot be the reason.

And why would one want to do away with the beneficial affects of overlap?

I completely agree with your post, and would add more.

Most of engine oil fowling comes from the piston cooling and lubrication. a 16.7:1 maintenance improvement is not credible.

Engines compression ratio is mainly governed by fuel octane level, for a given ignition advance and valve train timing.

If this were a really big improvement, the company would not need such a layman site to explain the benefits, and would rather have a strong technical demonstration.

A side by side comparison of similar engines with the regular and improved head would be a credibility improvement.

I ran a Ricardo variable compression engine in a university lab for many years. We could go up to 14:1 for gasoline and NG, 24:1 for diesel. The ignition timing was adjustable for +/-180° for TDC. The chamber was equipped with a pressure transducer and with the crankshaft encoder, the Otto P/V diagram could be optimised with an oscilloscope.

Lets say that some possible operating conditions were, far, far from stoichiometric...

I could see added flexibility in the infinitely variable valve timing this would permit, and provide a good proving ground for this technology.

So for Gensets, which run at peak load; stable and infinite adjust-ability would make it easily adaptable, right? Say I want to use an out of patent 12 cylinder engine block...

re-cast them and use this head... on LNG.

Less moving parts, less friction, less mean-time, between-failure.

Ah! If it were true!

Also, lets say LNG is a whole different ball bame than NG.

Variable intake and exhaust timing is very usefull for variable operating conditions, like car engines.

I am not convinced it would be much help for constant operating conditions.

Nice answer. I seem to remember that Ducati used to use "desmotronic" valves on their motorcycle. Were these rotary valves? Are they still using them? Do you have any additional information on the cam-less engine that used solenoids to operate the valves?

It's "desmodromic" - see Ducati Desmodromic Valves, for example - and they are conventional poppet valves, but they use cams and rockers to CLOSE as well as open, eliminating the spring(s) and their forces, theoretically eliminating valve float, etc. Other companies have also pursued this, but there are a lot of compromises, and it is only worthwhile for very special situations such as racing. Patents go back to 1896 - see http://en.wikipedia.org/wiki/Desmodromic_valve.

The other was a Lucas project using a device they called "Helinoid" read the response from "Danger" on Helinoid, or Google the term.

"The other was a Lucas project using a device they called "Helinoid" read the 2nd response from "Danger" on Helinoid, or Google the term."

Also written "helenoid" - e.g., helenoid. The "colenoid" is a similar / related device that was also tried for the same purpose: colenoid. Or search either term.

I looked at a couple more videos, both of which seemed fraudulent: in one, the elder Coates claims that no oil changes whatsoever are required; in another he claims that the engine emits "zero" emissions of two pollutant types -- obviously false.

The whole site seemed so fishy that I Googled "Coates fraud" and came up with this article from the New York Times.

Well-to-Wire Energy has this site which has not been updated in years. It seems WWE exists just to have a "customer" for Coates.

In an SEC filing, Coates states that the elder has been working on this since 1970. 38 years without every producing an engine that works as advertised. Many millions from investors apparently down the drain.

What a world.

Great job Ken, you got the eyeto find foolishness and scams!

The technology may be plagued with the same wear problems the Wankel engine has.

SUDDEN OPENING AND CLOSING OF VALVES AT THE EXACT TDC AND BDC WILL CREATE SHOCK WHILE ADMITTING MIXTURE INSIDE & SENDING EXHAUST GASES OUTSIDE, WHICH IS NOT PREFERED FOR THE OPERATION OF DG SETS.SHOCK OR VIBRATION IN ANY FORM IS TO BE AVOIDED FOR ANY MACHINE TO PERFORM SMOOTHLY.IN ADDITION TO IT, MORE OPENING AND CLOSING PERIODS OF VALVES IMPROVES THE VOLUMETRIC EFFICIENCY OF THE ENGINE.THE INCOMING MIXTURE GETS HEATED UP WHILE COMING IN CONTACT WITH THE HOT GASES AND THIS IMPROVES THE PROPER MIXING WITH THE FUEL AND THE HOT,LIGHT GASES ARE SCAVENGED EFFECTIVELY WITH THE HELP OF THE COLD, DENSE INCOMING MIXTURE/AIR.

My apologies if I've upset anyone with a propensity towards the use of absolutes.

I personally, feel this design may be reasonable, for a "might fine aircraft engine", (with proper British Management, of course).