Hot Bulb and Glow Plug Difference
|David Cambridge||30/12/2015 09:49:58|
|252 forum posts|
I’ve been marvelling at the various engines made by Find Hansen. One thought that occurred to me, and at least conceptually, is there any difference between a hot bulb engine and a glow plug engine ?
19084 forum posts
Glow plug gets its heat from the actual combustion once the engine is running, Hot Bulb needs a continuous heat source.
|Roderick Jenkins||30/12/2015 10:19:16|
1965 forum posts
Model aircraft type glow plugs only work with methanol fuels. The platinum coil in the plug catalyses a reaction with residual fuel to keep the coil hot between cycles.
Vehicle diesel glow plugs are just an aid to cold starting.
I guess you could use a continually powered model type glow plug as an ignition source for a stationary type kerosene / petrol engine. Don't know how long the coil would last though.
|Speedy Builder5||30/12/2015 10:36:19|
|2143 forum posts|
Hot bulb - After initial (external) heat, derives it heat from combustion products and should not require continuous external heat.
|Ian S C||31/12/2015 09:10:16|
7468 forum posts
Engines with a hot bulb usually don't need continued use of a blow lamp, while engines with a hot tube need a constant flame.
Ian S C
|Nigel McBurney 1||31/12/2015 09:56:22|
761 forum posts
Hot bulb engines eg Hornsby and Blackstone being the most common require a lamp to heat the hot bulb,the lamp is usually kept alight for a short time after starting, The Hornsby has the fuel injected into the hot bulb by a low pressure system which on the INDUCTION stroke shoots a jet of fuel across the inside of the hot bulb it hits the opposite side and vaporises,on the same stroke fresh air is drawn into the cylinder via the inlet valve,and does not travel through the hot bulb,the hot bulb is connected to the cylinder by a narrow passage the of this neck is critical, on compression the air and the rich fuel vapour mix and ignite,there is no timing as such,some control can be obtained by regulating the amount of fuel injected and the cooling water temperature. The Blackstone has two coaxial chambers the fuel is sucked into the outer chamber where it vaporises and then is drawn into the inner chamber via a timed inlet valve,fresh air is inducted directly into the cylinder and again only mixes with the vapour on the compression stroke.Very nice engines,I have nearly completely restored the smallest Blackstone hot bulb a 2hp ,though it still weighs several hundredweight. Hot tube ignition requires a continuous lamp to keep the tube very hot,unlike hot bulb engines which run on paraffin and heavier oils,hot tube ignition can be used on gas engines,petrol engines,and some paraffin engines where the heat from the lamp also heats a vaporiser. Most commonly seen are National,Crossley and Gardner. The hot bulb engine was developed as a means of running an engine on a "safe" fuel i.e. paraffin plus lamp oil was readily available around the world,insurance companies did not like engines running on benzine and petrol in buildings. Ignition timing of hot tube engines could be controlled approximately by the position of the lamp on the tube,close to the head advanced the ignition,one snag with gas engines was that if the engine stopped in a position where the inlet gas valve is open ,the leaking gas goes up inflames as it is ignited by the hot tube flame,one cannot leave a Gardner unattended on the rallyfield, Gas engines can easily be recognised by their three valves, gas,air and exhaust. The accidental barbecue from a gas engine was resolved when the ignition was provided by magneto,it also saved the gas used to keep the tube hot. Got to get back to the Blackstone.
|David Cambridge||01/01/2016 15:23:47|
|252 forum posts|
Lots of really useful information there, thanks everyone!
|Bob Rodgerson||01/01/2016 16:39:15|
|595 forum posts|
Hot bulb ignition engines were probably a good alternative to the early deisel engines that were Naturally aspirated and had a massive compressor that provided compressed air for the air blast injection systems that were used prior to direct injection. The latter system allowed development of smaller more powerfull engines
|Stuart Bridger||01/01/2016 18:57:38|
|488 forum posts|
The Bolinder hot bulb engines (usually deployed in marine applications) had an interesting injector design. The fuel spray could be varied much like a garden hose nozzle. Under heavy load, the it would be set for a fine jet, that went straight through the bulb chamber into the cylinder. Under light load or idling, the jet was adjusted into a broad cone, that sprayed the fuel onto the walls of the bulb chamber to keep it hot.
|Jens Eirik Skogstad||01/01/2016 21:56:53|
395 forum posts
There are three types of semi diesel engine that I know.. (Norway was the last country that produced semi diesel engines until 1968, also we had about 120 semi diesel engine factory in Norway).
1. Semi Diesel/hot bulb engine with low compression needs continuous heating of blowtorch (mostly older hot bulb egine).
2. Semi Diesel engine with medium-high compression needed not continuous heating due heat from combustion.
3. Semi Diesel engine with higher compression did not have great hot bulb. There are two ways to start the engine with the heated hot bulb or from electric glow plug. Forexample Wichman engine had only a slight glow ring around not long from the injector inside the cylinder head and heated via channel where the flame from torch lamp went into the channel and out of the other of channel such glow ring was hot enough to ignite the fuel under starting the engine. This type was called "cold cylinder head".
Edited By Jens Eirik Skogstad on 01/01/2016 22:15:24
|Jens Eirik Skogstad||01/01/2016 22:10:42|
395 forum posts
Before we got adjustable injector to regulate the fuel from thinn fuel jet to atomized fuel in semidiesel engine to prevent the engine is knocking under load and keep engine hot under idling. The engine had water injection under load and under idling no water injected into cylinder head. Problem was rust inside and in case water was empty then the fishing boat ran on idling at way home.
And we has a adjusting screw (Note: not speed regulator to regulate revolution of engine) to regulate fuel pump amount under load: If hot bulb is glowing under load ---> adjust the fuelpump to give amount lower. Correct temperature in hot bulb ---> take matchstick and touch on hot bulb. If machstick lighting up ----> correct temperature. Also no glowing hot bulb under load. (not for low compression semi diesel who need continous heat from torchlamp).
|Ian S C||02/01/2016 08:50:45|
7468 forum posts
The hot bulb engine that I have a little experience with is the Lanze Bulldog tractor (I suppose you include the whole tractor/engine), this engine is a 2 stroke. A common event a A&P shows, and other gatherings of tractors is a tractor starting competition, gentlemen, light your blow lamp.
Ian S C
|Danny M2Z||02/01/2016 09:21:50|
892 forum posts
One thing that may complicate matters was when O.S. introduced a model engine that runs on petrol yet uses a glowplug for ignition. I suspect that it uses a heavy coil to retain the heat. **LINK** . Interesting!
* Danny M *
Edited By Danny M2Z on 02/01/2016 09:23:10
|John Lovegrove||22/04/2018 16:21:56|
|7 forum posts|
I am a retired engineer, formerly from England, now living in Canada, and my main model engineering interest is building model internal combustion engines. I used to subscribe to Model Engineer but the distribution in Canada became screwed up and I let the subscription lapse. (Our club now subscribes to Model Engineer' Workshop.)
As my next project I am planning to try a hot bulb/semi diesel engine and over the years I have been assembling information on these. In fact this has taken on a life of its own.
I know that Find Hansen in Denmark has made some of these and someone told me recently that something appeared in Model Engineer earlier this year about building one. Could anyone comment on this?
One of the things I have been trying to properly understand is the approaches used to cover a range of engine loads: Stuart Bridger posted some information about what Bolinder did in their later engines. I was aware of this system but do not have many details. The Lanz Buldog tractors had a somewhat similar arrangement but it worked the other way around.
Anyway, if anyone would like to get involved with a discussion around hot bulb/semi diesel technology I would be very interested.
|Roger B||23/04/2018 12:58:38|
107 forum posts
My current interest is in full diesels but some of my future plans involve hot bulb/hot tube. I have collected some information that may be of interest:
Alyn Foundry produced a working version.
They are no longer trading but the original owner is active on Model Engine Maker as am I.
Some Italians have been making working models of Lanz Bulldogs and there variants such as Landini.
I also have a copy of the German book:
Lanz. Kühler-Bulldogs von 1928-1942. By Kurt Häfner.
This contains a lot of technical details including the different cylinder head designs used for different fuels and the injection system including the petrol injection, spark ignition starting system.
I hope that some of this may be of interest.
|John Lovegrove||23/04/2018 16:13:55|
|7 forum posts|
I did not know about the models made in Italy, the craftsmanship looks to be extremely good.
Someone fairly close to us has a Lanz Bulldog tractor (1949 I think.) I have seen this working and actually driven it. I have also made copies of the various manuals he has. Along the way I have acquired a couple of books on the Lanz but not the one you have.
While in the UK I have visited the Museum of internal Fire and the Anson Engine Museum, both places have several hot bulb/semi diesel engines operating. (Anson has several very interesting ones that are not running.)
I have assembled some information on American made engines and there are several operating in museums over here (e.g. Coolspring.)
Where I am really lacking is on information about the Scandinavian engines thinking particularly about Bolinder which was a major manufacturer and where it is hard to to find very much on all the development work they must have done.
The other area where I have assembled quite a lot of information is on the early work done by Akroyd Stuart. Here there is quite a lot of literature, but you have do dig fairly deeply to find items of significance.
Anyway.. I am very happy to swop information with anyone who is interested.
|Roger B||24/04/2018 11:41:21|
107 forum posts
I checked when I got home last night and found I had quoted the wrong book. The fuel system is in “Lanz von 1859 bis 1929” the previous volume by the same author.
The opposite adjustment of the injectors for the Lanz and Bolinder engines is due to the different layouts.
The Lanz injects across the hot bulb into a well. When idling the fuel jet is narrowed so it just goes into the well where it is vaporised and ignited. This small well will stay hot enough to maintain ignition. Under load the fuel jet is widened so that the fuel hits a wider area of the hot bulb giving a larger area for heat loss. The book notes that if the driver did not widen the jet when running under load the engine would suffer from pre-ignition and loss of power. If the jet was not then narrowed when the load was removed the bulb would cool and the engine would stop. A few minutes at the “wrong” setting was not a problem.
As Stuart Bridger notes the Bolinder injected through the hot bulb into the cylinder so in this case widening the jet will cause it to impinge on the hot bulb heating it up for slow running. Narrowing the jet allows it into the (water cooled) cylinder when under load.
|John Lovegrove||25/04/2018 03:26:03|
|7 forum posts|
Thanks again Roger,
I started a reply earlier but had problems adding a photograph, then lost everything - so I will start again.
The information I have on the Lanz says essentially the same but in much less detail. I have also been trying to fill out the picture on use of petrol in these engines. They seem to have a version to run on this on a normal basis (although it is hard to imagine why anyone would want to do so.) What seems to have been more normal is using petrol to start up, then switch over to a heavier fuel once the key parts were hot enough - avoiding the need to use a blowlamp to heat the bulb. My understanding is that petrol was injected using the same injector system as the normal fuel and that they had a spark plug giving a continuous stream of sparks (like one gets from a trembler coil) so that ignition occurred when enough air had entered the head section to form a combustible mixture. I did talk to someone who has a lot of experience with these tractors and apparently this was hard on the engine and crankshafts have been bent or broken using this method of starting.
Any comment on this would be appreciated.
A couple of other points where I have been trying to get more "solid" information are compression ratio and injection timing: I have seen numbers of 6 or 7 : 1 for the compression ratio an 160 deg. before TDC for the start of the injection. Again any comment would be appreciated.
Turning to the Bolinder engine: I do have a manual for their B & W type engines and this shows essentially the same combustion chamber arrangement as your picture (but the design is slightly different.) This general arrangement seems to be the one they ended up with after a lot of development work and several different design iterations. Prior to this there was an E type (which is like the illustration in the Wikipedia article on hot bulb engines) and an M type that appeared ~ 1915. This had an air atomization system for the injected fuel. In the E type, water was used to suppress pre-ignition under load but there was a very clear incentive to avoid the need for this and the variable spray injector used in later designs seems to have achieved this objective.
One other thing they did to help maintain an adequate combustion chamber temperature during idling was to throttle the flow of scavenging air to the cylinder. This would have reduced the cooling effect of the incoming air. This approach was also used by Kahlenberg (and maybe others.)
What I have no been able to do is piece together the the chronology of these developments - and what else they might have done along the way. Again, information on compression ratios and injection timing are hard to come by. All the B & W manual mentions is injection starting about half way through the compression stroke. An estimate of compression ratio could be obtained by making a proper drawing from the sectional drawings given in the literature, then doing the calculations. But so far I have not done this.
I will try to figure out how to add pictures so I can share some of these but I will not try here and risk losing what I have posted so far.
Once again, any information you can provide to fill in the gaps in my understanding, would be appreciated.
|Ian S C||25/04/2018 10:09:22|
7468 forum posts
I have a hand book for the Lanz Bulldog, there are quite a few here in Canterbury(NZ), a friend has one, but hasn't run it much of late, too busy mucking about with his Chamberlin(spelling), and Fordson. I did have some of it scanned off, but it seems to have gone AWOL.
Ian S C
|Roger B||25/04/2018 14:57:22|
107 forum posts
The Lanz Bulldog was able to run on a wide range of fuels, some of which required different cylinder heads, water injection or fuel preheaters. This list gives some of the variations and is it is described as for a 45 HP Bulldog I would have to assume it was a 10 litre engine. This would give a range of compression ratios from about 6-1 to over 10-1. The book suggests the normal compression ratios were between 5-1 and 6.5-1.
Injection timing is also a little difficult to define. The injection pumps were driven by eccentrics and in the case of the early engines the stroke of the pump was adjusted by a moving wedge which would alter the timing. The later engines moved the axis of the eccentric which would have a similar effect. Kurt Häfner states the timing as 120° to 135° before TDC.
The early tractors had an electrically assisted start system using an electric glowplug and a separate fuel pump and injector for what was described as ‘light oil’. The engine was still turned over by hand using the steering wheel. As you say the later tractors, especially the road haulage ones (Eil Bulldogs) used petrol in the second injection system and a sparking plug and trembler coil together with an electric starter motor. In both case when warm the engine was switched back to heavy oil. The units with an electric starter had a rev counter with a red area below 0 to warn you that the engine had started running in the wrong direction. It was assumed that if you had hand started the engine you should know this anyway.
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