Hot Tube Ignition and Other Early Daimler Engineering
Engine – Hot Tube Ignition
The Trust’s 1897 Daimler Grafton Phaeton is one of the first cars built in Britain. Lanchester built a prototype car in 1896 and The British Daimler Co started building cars in 1896 with the first production cars appearing in 1897. This was long before the mechanical layout of cars started to be standardised and much of the engineering used was in its infancy.
This car has a 2 cylinder engine of 1,527 cc developing 4 horsepower. The cylinders are cast iron, cast as a pair at the Daimler works in Cannstatt in Germany and imported to England as part of the licensing deal agreed between Frederick Simms and Gottlieb Daimler in Germany.
The engine is fed with fuel from an early design ‘surface’ carburettor allowing the fuel to evaporate and the fuel/air mixture to be drawn into the engine.
The ignition system pre-dates the advent of spark plug ignition and the fuel/air mixture is ignited by a ‘hot-tube’ system invented and patented by Gottlieb Daimler in 1883, initially for use in gas engines. This had been used by Daimler to power his initial ‘riding car’ of 1885.
- To start the car it is necessary to start a small fire in the ‘firebox’ beside the engine, where two bunsen type burners heat up a platinum tube until the end of it becomes red hot.
- This tube extends into the combustion chamber and on the compression stroke, the fuel/air mixture is pushed along the tube until it reaches the red hot spot and ignites.
- The burners are initially lit using methylated spirits and then, once hot, are fed from the normal petrol supply.
- The doors to the firebox are kept closed when driving, to shield the flames and stop them being blown out.
- If they do blow out, the engine will stop and the fire has to be re-lit before the engine will start again.
Disadvantages of hot-tube ignition
Hot-tube ignition had many problems, most caused by the sudden pressure changes in the tube because of the operation of the engine and the tube’s high temperature. While the hot-tube setup was relatively foolproof, the main drawback of the system is that there was no accurate way to time the ignition to ensure the fire occurs at the same instant each cycle.
It was also extremely difficult to find materials that were both durable enough for these conditions and inexpensive. The tubes used were typically 6 to 12 inches (15 to 30 cm) long, which tended to make them impractical for use on anything but large engines. Tubes rarely lasted longer than a year before needing replacement, especially when the engines were fuelled with high sulfur fuel.
It was also important to make sure that the tube never became white hot as this would rapidly damage the tube and could cause it to burst explosively.
By 1898, Daimler in Cannstatt had started to replace hot-tube ignition with spark ignition, powered either by a trembler coil, or, later a magneto. For a few years some cars were fitted with both systems but by the early 1900s the use of hot-tube ignition had ceased completely.
When the Daimler Grafton Phaeton was built in 1897 it was fitted with simple tiller steering. It was returned to the factory in 1899 to be fitted with the new-fangled steering wheel configuration that had been used on French Panhards since 1894.
There is a patch riveted onto the bonnet, in front of the windscreen, which covers the hole where the original steering column rose vertically.
The steering is very direct with about 1 turn from lock to lock.
This car was built before the layout of car controls became standardised, having 2 pedals, a throttle lever and an unusual two-lever gearchange.
- The left pedal operates the clutch.
- The right pedal operates the transmission brake.
- The hand operated lever between the pedals is the ‘governor’ – effectively the throttle.
- A small extra foot operated ‘button’ rings a warning bell – which is supplemented by a traditional rubber bulb operated klaxon type of horn.
The car has two gear quadrant levers, mounted vertically next to the steering column.
- The left one selects forward / reverse.
- The right one selects gears 1 to 4.
It is possible (but not advisable) to drive the car in reverse in 4th gear!
Wheels and Tyres
The wheels are traditional wooden spoked artillery or cart wheels with a wooden rim and an outer iron rim, and wooden hub with metal bearings.
Storing the cars in air conditioned museums causes the wood in the wheels to dry out and shrink, and the spokes can work loose. Before taking the Daimler (and the Trust’s other wooden wheeled veteran cars) out for a drive, we give the wheels a good soaking, so that the wood swells and the spokes fit properly.
The tyres are solid rubber, formed from long strips, wrapped around the iron rim and joined together with metal plates, and nuts and bolts.
In 1897 pneumatic tyres were in their infancy and were not fitted on Daimler cars until 1900.
This car has two braking systems:
- The right pedal operates a band brake working on the transmission which only slows the car down if it is in gear.
- The long lever to the right of the driver’s seat, operates the brakes working only on the rear wheels.
- Pushing it forwards, pulls the external brakes onto the outer edge of the rear tyres.
- These are not independently adjustable so the brakes can pull to one side or the other.
- On early, pre-tarmaced, muddy, roads they would not have been very effective.
There is no normal handbrake or parking brake, just a metal ‘sprag’ or spike which can be lowered to jam between the cobbles to prevent the car from rolling backwards. This is only likely to be able to hold the car on a very gentle slope.
The 2 cylinder engine is in the front of the car, with a massive flywheel to smooth out the power strokes. The centrally mounted gearbox has four speeds and a separate reverse shaft. It has an integral differential with drive shafts on both sides of the car, each with chain-drive, to both the rear wheels.
The maximum speed in 4th gear is about 15 mph, which given the minimal nature of the braking system is more than fast enough.
Suspension is by elliptical cart springs on all four wheels.
On the 1897 Daimler there is a brass ‘bicycle pump’ resting on the dashboard which is for pumping petrol. It is used to pump air into the petrol tank to pressurise it, with a pressure gauge mounted on the dashboard to ensure the correct pressure is reached.
The air pressure in the tank then pushes the fuel through the fuel pipes to the carburettor.
Once the engine has warmed up and the car is moving, the pressure in the exhaust system operates a mechanical pump which takes over pressurising the petrol tank.
Just as there is no electrically operated ignition, there are no electric lights on the 1897 Daimler.
All four lamps, two front and two rear, are run on candle power. Candles are inserted into brass tubes with a brass collar around the top of the candle holding it in place. Red glass was inserted in the rear lamps. A long spring in the tube pushes the candles up as they burn.
There are reflectors mounted behind and beside the candle to project the light to some extent.
These gave out very little light and were only really meant to make the car visible to other people, rather than to light the way ahead.
There were of course, no brake lights or indicators and definitely no fog lights, either front or rear.
Elephant Hide Hood
The foldable hood was quoted in the sales literature as being made from ‘Elephant Hide’ which was quite common on carriages from the late Victorian period.
‘Elephant Hide’ does not come from elephants, it is just a very heavy-duty grade of leather, often imprinted with the grain of an Elephant skin.
No Elephants were harmed in the making of this or other early Daimlers.
Author: Tony Merrygold
© Text and Images – Jaguar Daimler Heritage Trust