How much 'parasitic load' does a camshaft represent?

I think that wanting to know how much of the power these components consume is a fair question and look forward to someone quantifying them myself. The valve springs will be an especialy interesting discussion in my mind as well, they are used to time shift and give back a large portion of the energy used to compressthem, just time /vector shifted.

However, these are not parasitic load,as they are part and parcel of the provision of the piston engines power. airconditioner, power steering pumps etc are parasitic in that they take power away from the piston engine for purposes other than the provision of output. thus parasitic.

milo

These losses are combined in the total mechanical losses of an engine. These total mechanical losses also contain for instance friction losses is the bearings, losses for driving engine driven pumps etc. The exact amount of power needed to drive the camshaft is of course dependant on the size of the engine, the load of the engine and the type of the engine.

Normally these mechanical losses are for all (both diesel and gas engines) about 30-33 % of the power supplied to the engine for non turbocharged engines and varying from 32 to 49 % (depending on the size and type of engine) of the power supplied to the engine for turbocharged engine.

Several engine manufacturers for the large type two-stroke crosshead engine have developed an engine which, under normal running conditions (not emergency operation) does not need a camshaft. The camshaft is replaced by an electronic version of the camshaft. The original camshaft is still present in the engine, but it is not being driven. Only for emergency operation the chain drive is connected and the camshaft can be used. I know MAN-B&W manufactures these engines as the ME-series.

I looked up MAN engines & MAN that's a big one!

When you say normal running is camshaft-less in normal conditions, I assume that (electronically fired) hydraulics are used instead.

So about a third of the power is lost mechanically overall! Does that include gearbox/transmission losses. I imagine the largest part is at the crank since the forces are heaviest there.

I quite like the idea of a crankless engine: opposing pistons in a single bore with a hydraulic or pnumatic pumpfitted between them. This is simpler & should have less loss -should it not?

Mechanical losses are only for the internals of the engine itself. Losses for a gearbox and clutch or other driving and driven equipment is not taken into consideration. So this calculation "stops" where the shaft leaves the engine, for instance after the flywheel.

So if you also calcute the mechanical losses in the gearbox, clutch, drivetrain / propeller this number will increase even more.

As far as I know only the bigger engines can be equipped with an electronic camshaft, but who knows, maybe in the future also the smaller engines (car and truck size) can be fitted with such a device. Also, as couple of years ago only the 2-stroke engines can be equipped with this electronic camshaft. Maybe the manufacturers have already developped a 4-stroke engine with this, but I'm not sure of that.

To answer your question how this works: most of the engines of that size are already operating with hydraulic (exhaust)valve actuators, and engines with common rail injection (CDI) also have electric, pneumatic or hydraulic actuators / valves in the fuel injection line before the injectors. I'm not sure of all the technical details, but it seems to me that mechanical operation of valves and fuel injectors is far more reliable than electronics. This electronic camshaft control module is fitted with a back-up module, so if the electronics fail, there is still a second control module available. If that one also fails the camshaft will be connected to the chaindrive and it is possible to run the engine with mechanically driven valves and injectors at reduced power (about 70% instead of 85-90%).

By the way the biggest loss of a piston-engine is the thermicall losses, which means the heat radiating from your engine, going out of the exhaust, cooling water and lube oil. These losses can vary from 50-55% for non-turbocharged engine to 32- >50% for turbocharged engines.

Interesting!

Can you tell me how come thermal (or thermicall?) losses are actually lower for turbo engines?

Also, I didn't know inlet/exhaust valves could be electromechachanically actuated - I thought the responce times would be too slow & not last long.

In the turbo the heat is recycled through the turbo.

& this is a bad thing - rducing efficiency. Hence intercooler used.

Oh, hang on... you mean heat become work instead of being wasted!

Woops :)

I guess having a turbo is a bit like having you engine run in a much more high pressure atmosphere.

The air is more readily drawn ito the cylinder, but there is more to overcome on the exhaust side also.

Then uz superchager!

It is true that the response time of actuated valves is lower than the response time of directly driven (mechanical) valves. For the moment these actuated valves are as far as I know only fitted on low-speed 2-stroke (marine) diesel engines, also because these engines normally have only one valve (exhaust valve). Also, these engines are running very slowly at maximum power, ranging from abt 75 - 150 rpm.

How these actuated valves and CDI works, see drawing at the top.

Thermal losses on a turbocharged engine are lower, because these losses are expressed in percentages. If you would express these in actual power (kW), there wouldn't be so much difference. The turbocharger uses hot exhaust gasses to compress intake / scavenging air up to 2.5/2.8 bar. The exhaust gasses are expanding, thus lowering the exhaust gas temperatures. The intake air temperature rises up to abt 160 DegrC (10 MW 2-Stroke MAN-B&W 5S50MC/6L60MC), and needs to be cooled down by the intercooler to abt 38 DegrC. One of the causes that the thermal efficiency (losses expressed in percentages of primary power), is that waste heat is being "recycled" to drive the T/C, instead of going down the exhaust.

Another manufacturer of these engine types is Sulzer, their name for these engines is IE.

Drawing enlarged! Taken from http://www.knvts.nl/S&W%20archief/Recente%20ontwikkeling%20scheepsdieselmotoren.pdf

Article is in dutch, but the pictures are clear enough.

Back to the original posters question, how much is power is lost in the valvetrain depends on the type of valvetrain. Is it an old school overhead valve setup with pushrods and rocker arms. If so, is it mechanical flat tappet, hydraulic flat tappet, mechanical roller or hydrualic roller? Maybe its an overhead cam setup? Is (are) the cam(s) chain driven, gear driven or belt driven? How much spring pressure is there.

Obviously, as a percentage of total power output, the losses do go down as displacement increases, all other things being equal (because more displacement has more potential for power)

However, I suspect that the losses at the cam due to friction are very small compared to other components. Remember, OHV cams run on a thin layer of oil between the cam and the cam bearings, sustained by hydraulic pressure. The area that the pushrod comes in contact with the lifters is maybe on average a square half inch (same with the pushrod/rocker arm interface). Modern rocker arms have needle bearings at the shaft mount and the tip. Compare that with losses due to running the air conditioner (up to 20 HP loss!), power steering pump, water pump, and alternator and you'll see cam losses are a drop in the bucket, even on a naturally aspirated engine.

As for drivetrain losses, its generally accepted that whatever you flywheel HP is, subtract 15% for a manual transmission drivetrain and 20% for an automatic drivetrain and thats roughly what to expect at the wheels.

Avery Montembeault

As for load a proper modern camshaft by itself has little drag. The mechanical Assembly turns a little into heat but as stated the springs compressed release forward motion they used back into the cam.

As for actuators bing slow

http://en.wikipedia.org/wiki/Formula_One_car

For a decade F1 cars had run with 3.0 litre naturally-aspirated V10 engines, but in an attempt to slow the cars down, the FIA mandated that as of the 2006 season the cars must be powered by 2.4 litre naturally-aspirated engines in the V8 configuration that have no more than four valves per cylinder. Further technical restrictions such as a ban on variable intake trumpets have also been introduced with the new 2.4 L V8 formula to prevent the teams from achieving higher rpm and horsepower too quickly. As of the start of the 2007 season all engines are now limited to 19,000 rpm in an effort to improve engine reliability and to cut costs down in general.

Once the teams started using exotic alloys in the late 1990s, the FIA banned the use of exotic materials in engine construction, and only aluminum and iron alloys were allowed for the pistons, cylinders, connecting rods, and crankshafts. Nevertheless through engineering on the limit and the use of such devices as pneumatic valves, modern F1 engines have revved up to over 18,000 rpm since approximately the 2000 season. Almost each year the FIA has enforced material and design restrictions to limit power, otherwise the 3.0L V10 engines would easily have exceeded 22,000 rpm^{[citation needed]} and well over 1,000 hp (745 kW)^{[citation needed]}. Even with the restrictions the V10s in the 2005 season were reputed to develop 960 hp (715 kW)^{[citation needed]}. The new 2.4L V8 engines are reported to develop between 700 hp (520 kW) and 780 hp (582 kW).^[citation

For a truly interesting valve system try http://www.coatesengine.com/

Brad

This article should give you an answer, although I just scanned it, and found that the key figure (Figure 7) seems to be missing -- however there are links to other articles that should provide details.

My gut level answer would be that not very much power is consumed by the valve train. The energy used in compressing a valve spring is returned as it expands (minus internal friction in the spring, and minus the cam-follower friction, valve stem friction, etc.) One can turn a well-worn engine (in which the ring pressures are low and cylinders are smooth) with the spark plugs out quite easily -- I'd guess about 5 lb ft would turn the flywheel in an engine designed to produce 100 lb ft. A small part of that is from the valve train, with the vast majority from the crank, rods and pistons. The piston ring friction increases with increasing cylinder pressure, whereas the valve train friction would be relatively constant. I'd guess 1% of the power is consumed in the valve train.

Thanks for the link. It looks like these loads are negligible in the overall scheme of things! When I first enquired I was considering the application of using a turbo, not to pressurise the inlet, but to run a hydraulic system... ???

not to pressurise the inlet, but to run a hydraulic system... ???

A good thought. In practice though, the imposition of a turbo in the exhaust system causes the engine to work harder to expel exhaust: the exhaust energy is really not free. So when you compare spark ignition turbos and competitive normally-aspirated engines, you find that once they are installed in comparable cars, all aspects of performance pretty well equalize. (The turbo system adds weight, but the engine can be smaller... the turbo adds back pressure, but this is compensated by increased output... etc.)

In this comparison test, the normally-aspirated cars perform best, with the Acura TL and BMW 330 out-accelerating the Volvo (which is turbocharged). All three have the same EPA highway ratings and all three have the same Edmunds observed fuel efficiency. The EPA city figure for the Volvo is slightly better, at 20 vs 19.

With diesels, the situation is a little different, with turbo diesels often getting slightly better brake specific fuel consumption (which measures the engine' fuel efficiency, independent of the car) figures than non turbo. That, combined with the lower weight of the engine, (being able to use a smaller engine for the same output) translates into better fuel mileage once the engine is installed in a vehicle. (Of course, diesels already have a significant advantage in efficiency over spark ignition engines, even when not turbocharged.)

On the other hand, BMW has worked on turbo-powered alternators, apparently with some success. It's interesting that alternators have been belt driven for many decades. On motorcycles, they are always directly driven from the crankshaft, so there is no transmission loss at all. (Traditionally, belt driven alternators are not very efficient [60 - 70% for the machine itself] and driving at higher speeds improves efficiency somewhat... so there are trade-offs.)

Extracting heat energy from the outside of the exhaust system is starting to show some promise, with a recent doubling of efficiency of heat-to-electricity devices (from awful to fairly poor).

But, in any case, good thoughts: there are all sorts of ways of improving the efficiency of automotive engines the we should be looking into.

Yes, indeed - Clearly turbo energy is not free - back pressure at the exhaust will make the engine work pumping air when it least needs to - ie. the exhaust stroke.

However, several factors have sprung to mind:

- If turbo engines do not offer substantially improved power-to-weight (& potentially better efficiency with good design) why have so many car manufacturers plump for them? Especially, considering the added complexity.

- Power delivery matching for cruising, acceleration, etc - These modes call for a very flexible power source, that the IC engine has made a good show of filling. But, as with the example of hybrids, storing some that energy may bring real-world advantages.

- Hydraulics & pneumatics are tried & tested technologies and accumulators are simple and can be made compact (not sure on weight comparisons with electric batteries?). Accumulators will last indefinitely and have no chemical waste products (Unlike batteries).

Here's a thought: A standard turbo with all but the lowest pressure will need a bypass valve, so as not to choke the engine at low revs. Could the valve, instead of venting pressure charge an accumulator via a suitably variable-load pump; not wanting to load-up the exhaust stroke unduly.

If nothing else the accumulator might be used to eliminate turbo lag - helping to spin up.

- If turbo engines do not offer substantially improved power-to-weight (& potentially better efficiency with good design) why have so many car manufacturers plump for them? Especially, considering the added complexity.

Good question. In aircraft, they make great sense, improving operating ceiling substantially, in a way that a larger engine cannot match. In cars, they are "pretty neat", and a great way to increase the hp and power-to-weight ratio of the engine itself, especially if the engine already exists, but are not used in the "pull out the stops" efficiency designs like the Prius or Honda Insight. (Although they are used in diesels where a key goal is fuel efficiency. There, they do very often improve efficiency (brake specific fuel consumption) in addition to engine power-to-weight ratio.

Manufacturers, many of whom are obsessive about cutting costs, have shown that turbos do not make sense economically on petrol engines: economy cars, standard sedans etc, mostly get their power, from displacement and the evolutionary techniques such as variable valve timing, four valves per cylinder, etc. Typically, the parts count is lower on a larger engine than on an engine equipped with a turbo. Thus we see turbos where image counts, and where there is an existing model to modify (Subaru WRX) and on premium cars (Volvos, Saabs, some Porsches) but not in Hondas, Toyotas, Nissans, Mazdas, Fords, etc.

With diesels, it's a different story, and normally-aspirated diesels are rare in cars, not being able to offer the performance people have come to expect.

In the S60, Volvo trades 5 cylinders and a turbo for the six cylinders of most of the competition, and effectively loses. Most people love BMW engines, and many people complain about the Volvo engine there's turbo lag, and the car is slower than many others and no cheaper. (I like Volvos and the people who make them , having worked on some new product launches for them, but once the whole package is put together, they don't quite match a BMW for the things people look for in this segment.)

Hi.

You mentioned a comparitive test: turbos versus N/As ("Acura TL and BMW 330 out-accelerating the Volvo")

Are details of this test available on-line?

Thanks

Ooops. Ordinarily where I wrote "in this comparison test" I would have made a link. The link is to one of many pages about the comparison test.

I wonder how the comparative losses of or standard drive-trains compare to a (crankless) piston engine actuating a pneumatic pump with an accmulator - to deliver power as necessary to pneumatic wheel motors?

Alternatively, hydaulics may be better, but I think they have more fluid 'drag'...

Is there any merit in these ideas?

I'm guessing not -or someone would have made a fortune with it by now!