Difference between 'Glühkopf' and 'halbdiesel' ?

[zeeman]

Hi !

Sorry if my question may seem silly to a Lanz connoisseur, but could someone please explain the difference between a 'Glühkopf' and a 'halbdiesel' Lanz to me?

Thanks.

[Chicken]

Hi!

The "Halbdiesel" is more a true diesel engine and not a hot bulb engine. The classic Lanz hotbulb engine (Glühkopf) has a low compression (7:1) and a prechamber with the hotbulb. Fuel is injected about 160 ° before TDC with a very simple open injector at low pressures. The Glühkopf will run on any type of fuel.
The Halbdiesel (semi diesel) has much higher compression (13:1) does not have a prechamber and is directly injecting with a high presure injection system. Injection is also much later at about 20 ° before TDC. The fuel ignites due to the compression temperature assisted by the warm walls of the cylinder head which is only poorly cooled and the warm piston.
The "Halbdiesels" were usually started with a gas/diesel mixture using an electric spark.
The last engines, the "Volldiesel" (= full diesel) were basically the same engines as the halbdiesel, but were startet directly with diesel fuel and a glow plug as assistance.
The halb and volldiesel engines will only run on diesel, they do not tolerate all sorts of different fuels like the true hot bulb engine.

[bulldogfan]

chicken's explanation is all good and well, but both engines remain diesel engines and are essentially the same. one's a bit better than the other, that's the main difference really

[Chicken]

Hi!

The hotbulb engine is no diesel engine although today it is usually run with diesel!

[bulldogfan]

sorry, but it's got nothing to do with whether it runs on diesel or junglejuice.
the fuel is ignited only by compression and that's imho the definition of diesel engine.

[Chicken]

sorry but that's wrong.
The hot bulb engine ignites the fuel by the glowing walls of the hot bulb and not by compression temperature. Compression of 6-7:1 (which is less than a modern gasoline engine) is far too low to ignite diesel. That's why you either have to heat the hot bulb to a temperature above the ignition point of diesel (about 250...400 °C so red glowing) , or start the engine with gasoline and electric spark.
the hot bulb engine is definitively no diesel engine. It is more or less a mixture of diesel and gasoline engine:
The fuel injection is similar to a diesel engine. Compression ratio and the clearly differentiated injection and combustion times are similar to a gasoline engine.
You can read about this in almost all scientific papers, that the hot bulb engine is no diesel engine!

[bulldogfan]

let's agree to disagree

[Theo S.]

This discussion gives a good impression over the fact that for "specialists" it is not always clear that a hot bulb engine is not a diesel engine. Why it would be called also otherwise hot bulb engine.

[bulldogfan]

Hi,

I'm no specialist and never claimed to be one. However, Lanz called it's 'hotbulb' engine 'semi diesel'. I'm not really sure what a 'semi diesel' actually is......and i have never heard of a specialist that could define it either, but maybe you can?

What is commonly known as 'Halbdiesel' has a hot bulb too, the only difference is that it's smaller and you can't blow torch it. So please explain as to where the difference between a hotbulb and a halbdiesel is if they both have a hotbulb? A 'Volldiesel' is considered a 'Diesel' even though there actually is no difference to the the Halbdiesel. Yes, i know that the cylinder head cooling system is slightly revised and the compression is slightly raised, meaning that more heat is generated during compression and therefore less heat needs to be stored elsewhere in the combustion chamber, but none of that has any effect on the basic combustion/ignition principle. If you want to be consistent, they are all either 'Hotbulb' engines or 'Diesel', but you can't have it both ways.

A 'Halbdiesel' was called Diesel by Lanz (most likely because that's what it is)

[Chicken]

Lanz never called its hotbulb engines semi diesel.
Semi diesels were the "Halbdiesel" engines. The Halbdiesel does not have a hot bulb and also no prechamber, it is a completely different engine compared to the hotbulb engine and is a true diesel engine. Every halbdiesel bulldog can be converted to glow plug ignition for starting without many problems.

[Theo S.]

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

[patfinistere]

Oh dear pressure seems to be mounting in this particular cylinder!

Let no one call me an expert, I have a number of Lanz, both hotbulb and later non hotbulb engined tractors. I also have a "Le Percheron" and Société Française Vierzon hotbulb tractors.

Up until this posting I have called my hotbulb engines "Semidiesel" and the non hotbulb engines diesel.

Now I am not sure!!!

Fortunately I have the original instruction book that came with my 5506 (hotbulb and trembler-coil ignition) of 1952, on page 172 the "details techniques" state:- (and I translate from the French)
'Monocylinder horizontal engine, twostroke, medium compression with ignition by hotbulb without valves, without carburettor.......'
The instructions in English for the 7506/8506 etc. read almost exactly the same.
So No mention of Semi Diesel for the hotbulb engine.

At present I have lent my instructions for the 2416/2816 series to someone so that I am unable to verify what it says for these, what I would call "Full Diesel" engines.

I call them that as they resemble the modern day diesel engine in that there is no need for an outside heat source to start the engine, except as in most modern diesel engines, a glow plug when the engine is cold.

However I have also a publicity booklet in French for the "New Lanz Engine of 17 HP", that is to say the 5506 without hotbulb. In this booklet the new 17cv engine is stated as a "Medium Compression" engine..with a new combustion chamber and a compression ratio of 10:1.

You will see that this is still called a "medium Compression" engine, even though it is a "Full Diesel".

Could the term semidiesel be an invented term that Heinrich never used?

It would be interesting if some greater authority than myself could look at some of the earlier literature produced by Lanz, especially in the original German.

Interesting debate.

Pat