Tiny diesels question

I remember seeing small model Diesel aero-engines of around 1cc displacement, these were, of course, 2 stroke with crankcase compression and run on a paraffin / castor oil / ether mix and use a carburettor. I guess from the phrasing of the question you are talking about 4 stroke direct injected Diesels (by direct I mean either into the main cylinder or into a swirl chamber). Martin

The smallest one I know about is the Dux designed and built by Martin Alewijn from Holland. The full plans were published in Strictly IC. Although Strictly IC is no longer published, all back issues are still available. I started to build the Dux, but haven't had time to do much to it recently. If you goto my website

Moray

Look back to last October to the thread entitled "Deltic model".

Cliff Coggin Kent UK

Indeed I am talking about multiple-cyclinder 4-stroke with direct cyclinder injection. I imagine it would be a bugger to make HP injectors for anything smaller than 0.75cc...!

I should have mentioned that! ^_^

Thanks for the info.

Okay, will-do.

I think most of the engines used by model aircraft are technically diesels...

Wasn't that actually spark ignition? (Incredible bit of modelling though)

The bore is 22mm with a stroke of 24mm.

The problem with diesel injections engines this small, is the fuel supply. The main problem being getting an injector with a small enough hole. Martin Alewijn solved this by not having any moving parts in the injector. His nozzle was created by having the end consist of two cones that screwed together. A scratch is then made on the inner cone before assembly, which provides a suitable sized orifice to atomize the minute amount of fuel needed for the engine to run. The injection pump is made by reaming a 2mm bore into the steel injection pump body. The piston is made by taking a piece off 2mm silver steel, and slitting the end off, which helps create a better seal for pumping the fuel.

moray

Indeed it is. I wonder if he's completed the 180,000 sparks/min mechanism he required?!

Getting back to the thread though, one cyclinder in that mini-Deltic equates to around 8cc, which is still a bit large for what I'm envisaging (if there is such a word).

I know you can build miniscule working steam plants (Tubal Cain springs to mind!), but that's a different principal and I'm beginning to think that the reason no-one has seen *really* small diesel engines is because there aren't any!

Ah well, 'twas worth a try. Thanks for your help folks. :¬)

Main reason there isn't any that small is because they quite simply wouldn't run. The smaller you make the cylinder, the harder it becomes to heat the compressed air enough, so that the injected diesel will self ignite. This is all explained in the Dux article in Strictly IC. Even if you don't build an engine, it is still a very good article to read, as it shows how a bit ingenuity can solve problems (such as the injector design).

moray

That is very ingenius!

It does indeed sound a good article and I'll read practically anything involving IC engines anyway! So I'll try to get a copy...

Thanks for your help on this, folks.

the smallest compression ignition diesel i have seen is the davies charlton bambi which was .15cc.a friend of mine regularly flies models with a scaled down mills engine which is .25cc

Although compression ignition engines they're not 'diesels'. A 'diesel' injects the fuel into the hot compressed air in the cylinder to initiate ignition. The miniature compression ignition engines take in the fuel mixed with the air and compress both together to get the ignition.

bolmas wrote:

thanks for the correction, so what are they called then

-- bolma

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Not necessarily have to inject into the cylinder you are wrong!

Might be a suitable role for machinable ceramics, to reduce cooling. (Though you still have to solve the fuel injection problem)

- Brian

Well...the injection of fuel into a cylinder that has already compressed (and therefore heated) a volume of air is (as I understand it - please correct me if I am mistaken here) an essential feature of the Diesel patent. The point being that the superior efficiency of a Diesel engine is in part related to the high compression ratios that can be used if you inject the fuel into a compressed volume of hot air. If you mix the fuel/air first & then compress it (as is done in the model compression ignition engines), then you cannot use such high compression ratios without the mixture igniting prematurely & resulting in "knocking" or even worse, misfiring and the engine not running at all.

So the model CI engines are not Diesels in that sense, although they are often referred to (incorrectly, it would seem) as Diesels.

Its a bit like all vacuum cleaners being known colloquially as Hoovers; clearly, a Dyson is a vacuum cleaner, but it isn't a Hoover (although sometimes, both Hoovers and Dysons are washing machines...).

But when all's said & done, Hoover hell cares??

Regards, Tony