Blowpipe (induced draft)
As blowing tube is according to the principle of a steam jet blower functioning exhaust installation of a boiler, particularly in steam engines , respectively.
General
The induced draft system is the heart of a steam locomotive: It drives material turnover, combustion and convective heat transfer in the boiler and regulates the boiler output according to the needs of the steam engine. This is what makes the locomotives' high performance compared to stationary steam engines possible in the first place. To do this, the induced draft system uses a considerable part of the expansion energy of the steam power process, which is lost again from the effective locomotive power. The proportion increases disproportionately with the power density of the boiler, so that the efficiency of the induced draft system is of particular importance in order to achieve a powerful and economical locomotive. The actual execution is always a compromise.
Since the system has to work in heat, dirt and aggressive media, turbo blowers have not been able to prevail against the robust blowpipes despite their higher efficiency.
functionality
The exhaust steam from the locomotive cylinders is used as the driving medium for the jet fan. This is directed into the nozzle-shaped blowpipe, which stands vertically inside the smoke chamber at a certain distance below the chimney ( chimney ). The blowpipe axis and the chimney axis must coincide exactly. The chimney widens slightly conically towards the top and its diameter is adapted to the blowpipe diameter so that the exhaust steam flowing out of the blowpipe completely fills the chimney from approximately the middle to the top. The escaping steam then exerts a suction effect on the surroundings of the blowpipe. Since the smoke chamber is completely airtight, the sucking steam flow in the smoke chamber creates a negative pressure, which now sucks air into the smoke chamber via the only remaining path, namely through the air flaps of the ash pan , the grate, the fire layer and the heating and smoke pipes . The air flowing in through the ash box supplies the fuel bed with the oxygen required for combustion.
In particular, the fact that the suction effect, and thus the fanning of the fire, is greater, the more steam is used for propulsion, is advantageous. Thus it is possible (within certain limits) to bring fuel into the boiler 'in reserve', even if the additional energy is only required later, whereby the heater and the like. U. can be relieved considerably.
When the locomotive is at a standstill and when the fire is started, the induced draft can be generated with the auxiliary blower .
history
The blowpipe was invented in 1801 by Richard Trevithick , the British pioneer of steam locomotive technology, and was first installed in his steam car . A little later, Timothy Hackworth and George Stephenson also used this technology in their locomotives, although it is unclear whether they were aware of Trevithick's invention or developed it independently. Later on, blowguns became the standard for almost all steam locomotives. The system remained largely unchanged for nearly 100 years.
From around 1900 there were tendencies to improve the efficiency and performance of the blowpipe, to reduce the counter pressure for the cylinders in order to achieve maximum energy yield for the drive and at the same time to get the best possible negative pressure in the smoke chamber. For this purpose, the blowpipes were designed to be adjustable and various variants of series and parallel connection of jet fans were used:
- Kylchap by the Finnish engineer Kylälä and the French engineer André Chapelon
- Lemaître blowpipe , Lempor and Lemprex by Jean Lemaître and Livio Dante Porta
- Giesl ejector from Dr. Adolph Giesl-Gieslingen
In the case of the condensing locomotive, the blowpipe was finally replaced by a fan with a steam turbine drive. The exhaust steam from the cylinders was condensed and thus recovered to replenish the water supply instead of being blown into the atmosphere. This minimized water consumption and maximized energy efficiency.
Individual evidence
- ↑ Bruno Lämmli: The smoke chamber. In: Lokifahrer. 2014, accessed October 13, 2018 .