Cylinder deactivation or Cylinder on demand (CoD)

[desperatelyseeking]

I note that VW has introduced a new engine on the latest golf. At lower power demands ie motorway cruising, the engine shuts down 2 of the four cylinders greatly increasing economy, when power demand is increased the cylinders reactivate.

Seems to me that this would work very well in the marine environment, particularly for semi displacement boats.
1. You could have large HP engines that are very efficient at displacement cruising speeds but have the power if you want to get cracking on
2. Would enable the installantion of a single large engine reducing build costs, servicing costs, drag of two props

I think the idea of having a "jeckle and hyde" engine that can be both a very economical low powered unit and have the capability of giving substantially more power on the occasions you need it would be very popular. Given that VW is already a player in the marine industry anyone know if they have deployed this technology yet? Are there reasons that this kind of system would not be practical in a boat?

 

[sarabande]

I can think of heating. If the cooling of a marine diesel is designed for all cylinders being operational, then when it's on say 2, the engine might be overcooled - unless of course the coolant system is also changed at the same time.

 

[NormanS]

Kelvin petrol /paraffin engines had that system yonks ago.

 

[Trundlebug]

I can think of heating. If the cooling of a marine diesel is designed for all cylinders being operational, then when it's on say 2, the engine might be overcooled - unless of course the coolant system is also changed at the same time.

The thermostat will take care of that, as it does in any case. I would imagine the cut-out would only activate once the engine is up to normal operating temperature.



To the OP, The only reason I can think of why it wouldn't be as practical in a boat is that engine loadings are considerably higher; there is contsant load on the engine because the drag is much greater. In a car, once it's up to speed the only drag is air resistance, much less than pushing a boat through water.

However I do agree that for displacement speeds and idling it could be worthwhile.

I think as fuel becomes ever more expensive all sorts of alternatives and tech advancements will be developed and introduced, e.g. catamarans, air hulls etc as well as engine developments like this

 

[desperatelyseeking]

I agree. I'm actually getting a bit "geeky" about the whole efficiency thing. Hull design, bulbous bow, stern vanes plus increased engine efficiency might actually make boating affordable again and save companies like Sealine going to the wall.

Maybe I'll have to become a motor sailor to achieve that retirement ambition of sailing round the world in 15 years!!

 

[jfm]

There are some myths here. To move a boat slowly may need 10% of the engine's max power output, say, but if you take that from all of the cylinders making 10% of max power compared with half the cylinders running at 20% doesn't change efficiency big time. Why would it? The parasytic drag inside the engine remains the same and the thermal efficiency in terms of converting joules of diesel fuel energy into joules of kinetic energy isn't much different. There may be some small differences, but they are very small

Now, if you can jam open the valves on the "dead" cylinders so there is no energy consumed in their compression stroke that's a somewhat different ballgame, but afaik that concept isn't being used in these "shut down half the cylinders" engines. Happy to be enlightened and corrected if I'm wrong on that

 

[Bandit]

MTU had that 20 years ago on tickover.

You can imagine problems with unequal hot spots on engines if you run at half power with only half of the cylinders firing?

 

[Spi D]

Kelvin petrol /paraffin engines had that system yonks ago.

Some Mercury 2-stroke outboards (like the 115) had that in early 90's an on until 4 strokes captured the market. Known as 2+2 where the 'on demand' trigger point was 1800 rpm.

 

[prv]

You can imagine problems with unequal hot spots on engines if you run at half power with only half of the cylinders firing?

Maybe the cylinders take it in turns to have a break? You'd want to do that to some extent anyway to even out the wear.

Pete

 

[ulyden]

Think this is possible. MTU have done this last 30years saving smoke emissions i think. Still they are using it.I was just on a boat with a 2.5MW genset. Problem was consumption at low load. Engine was consuming 100l/h with no load. Even this has cylinder cut or bank cut. To be able to have load on one bank the engine have to be built like to seperate inline engines. Most modern common rail engines used in commercial boats have this option to be able to cope with the rule of one fault should not stop the engine. If the rail is leaking, hp pump is gone or something is wrong with sensors the half of the engine will still run. Such engine have redundant eletrical controll systems. With a common rail engine skip fiering is also possible.

The VW system is maily used for cars. The fuel saving potensial is greatest at low engine load. A load most boats dont run that low. Below 50% engine speed.
The VW system is sofisticated and the loss off pumping work with two not working cylinders is low.

 

[burgundyben]

Now, if you can jam open the valves on the "dead" cylinders so there is no energy consumed in their compression stroke that's a somewhat different ballgame

But Shirley...the energy invested in compressing the gases in the cylinder is released back into the rotating assembly on the stroke back downwards? Long discussion on this very point on pistonheads, opinion seemed to be net loss not very big. Store. Release. Store. Release....

 

[gordmac]

I think American V8s have been doing this for decades. Doing it right is costly, car makers will do a lot of expensive things to meet emissions and get good fuel economy figures. Not such a motivation for boat engines.

 

[Latestarter1]

Now, if you can jam open the valves on the "dead" cylinders so there is no energy consumed in their compression stroke that's a somewhat different ballgame, but afaik that concept isn't being used in these "shut down half the cylinders" engines. Happy to be enlightened and corrected if I'm wrong on that

Kind of like a Jake brake..http://www.ask.com/wiki/Compression_release_engine_brake?o=3986&qsrc=999

Clessie Cummins actually first demonstrated his compression brake on his motor cruiser engines around 1960.

For a change I am in accord with Uliden, I experimented with cutting out cylinders at low engine load with first common rail motors in late 90's, cylinder cooling was an emissions issue however by constantly switching the pot you are cutting out you can keep temperature up. Fuel consumption benifits were lost in the noise and engine felt as rough as badgers bum when feature activated.

 

[rafiki_]

Agree with LS on this. Car manufacturers are doing this to eek out fantastic CO2 numbers on the Eu drive cycle, with no interest in real life fuel consumption.