myfordboy blog and online resources: The Essex Hot Air Engine

This engine was designed by Henry Essex and was patented in 1902 (US 723,660)

The engines were on sale around 1905 and were advertised as suitable for running fans, window displays, model machinery, peanut roasters and sewing machines.

Some models had a fan to cool the cold end of the cylinder driven from the engine flywheel, others had a water tank at the cold end. A twin cylinder version was also available.

The engine works on the Stirling cycle principle but is unusual in that the heat is applied to the centre of the engine rather than at one end.

Essex claimed greater efficiency was achieved with this layout.

The Replica Engine

My engine is a full size replica and was made from measurements taken from an actual Essex engine.

It is a great runner and will run unattended all day powered by butane gas from a camping type disposable cylinder.

There is a series of videos showing the full build.
Part 1 shows the cylinders being machined.
Part 2 covers the crankshaft bearing.
Part 3 shows the engine frame being machined.
Part 4 shows the furnace construction.
Part 5 making the burner.
Part 6 Making the cylinder liner.
Part 7 making the piston.
Part 8 Piston extention
Part 9 Turning the flywheel.
Part 10 The crankshaft.
Part 11The connecting rod
Part 12 The base
Part 13 The water jacket
Part 14 Displacer
Part 15 Finished engine

Part 1 video
The cylinders

Machined cylinders

How the water jacket is made

Two part wooden pattern

Core box

Sand core

Cast in sand

Finished casting

Watch the video of the water jacket

More engine details

The engine can be made on a lathe with a centre height of 3, 3/8" or more. You can see in the video it just goes in my Myford ML10.

Length 19, 1/4" ( 489mm)

Width 6, 1/8" ( 156mm)

Height 7" ( 178mm)

Flywheel diameter 6" (152mm)

Part built

Set of castings

Plans and instructions

Castings for sale

The set of 7 castings shown above together with full plans are available for £230.00 plus shipping. I can ship worldwide at a very reasonable cost. Also included are building notes, material list and photographs and ceramic material for the burner. To keep down costs, the cast base is not included. Many Essex engines were supplied without this and they would be mounted on a wooden base with the machinery they were driving.

To order please send email to the address at the bottom of this page and I will forward payment details.

Also available is a set of 4 casting to build the Essex turntable. Scroll down for further details.

As I have built 2 of these engines I would be prepared to sell the one shown here and constructed in the videos. Make me an offer.

Testimonials

" Wow, great castings, well packed, very satisfied"

Teun, The Netherlands

"What a fantastic job on the castings"

Ian, Australia

" Received the castings and instructions, looks great!"

Frank, USA

" The castings are lovely and the drawings being enclosed in plastic was an unexpected bonus"

Ken, Canada

" The package arrived as stated the next day.

All parts look good and I look forward to starting the project"

Henrik, Sweden.

" It is setting along side of my two original Essex engines. It looks and runs great, just like the originals do".

Barry, USA

"The castings and prints just arrived and I unpacked them. They are beautiful castings and well in the capabilities of my shop."

Brad, Wisconsin

"I must say I'm impressed with the speedy shipping and the quality of the castings. I've machined a lot of castings over years and these are some of the finest I've seen.

Thank you,"

Lonnie USA

How it works

As you can see in the drawing below, the Essex is a very simple engine with only 5 moving parts.

It follows the basic Stirling cycle in which air in a sealed cylinder is alternatively heated and cooled, which creates a rise in pressure when heated, and a fall when cooled. The rise and fall of pressure is used to move the piston of the engine.

A Stirling engine will have a hot end and a cold end. The hot end is heated and the cold end is kept cold, in this case by the water jacket and cooling fins.
As it is not practical to heat and then cool the cylinder rapidly, instead the air is moved between the hot and the cold end and this creates a rise and fall of pressure.
The air is moved by the use of the displacer. This is not a piston, it does not touch the sides of the cylinder but takes up space.
Imagine a jar with a lid and inside there is a smaller sealed jar about 3/4 the size.
When the small jar is resting on the bottom, most of the air inside the large one will be at the top. If the inside jar was now moved somehow to the top, the air would be displaced past it and most of the contained air is moved to the bottom.
In the drawing above the displacer is shown at the end of it's stroke and the piston is at it's mid position with the crankpin of the crankshaft at
12-O-Clock.
Heat is applied at the centre of the engine, the circle is the furnace .
The engine runs in a clockwise direction when viewed from the flywheel.
With the displacer in the position shown, the the air in the cylinder is heated and expands , moving the piston forwards. As the piston moves forwards the displacer is also moved forwards by the long connecting rod attached to the flywheel crank. This crank is 90 deg behind the crankshaft one.
As the the displacer moves forwards the air is moved to the cold end where the drop in temperature will cause a fall in pressure which will move the piston back into the cylinder. The cycle now repeats and the flywheel continues to rotate.
I hope I have given an explanation you can follow. It can be difficult to understand the principle and even more difficult trying to explain it!

Essex window display turntable

One of the uses for the Essex engine was to power a rotating turntable for shop window displays. Below is a photo of an original turntable.