What expansion ratio does the hyperexpansion engine in Patent 988,378 use?

The document states the expansion ratio may be of the order of 75:1 or higher, chosen so cylinder pressure at inlet port opening is below the supply air pressure and exhaust gas temperature is low enough to have a cooling effect.

How are the compression and expansion ratios defined in this patent?

The compression ratio is (v+Vc)/v and the expansion ratio is (v+Ve)/v, where v is the combustion chamber volume at top dead centre, Ve is the piston displacement at the point of inlet port opening, and Vc is the volume swept during the compression period.

What do the crank pin positions A, B, C, D and E represent in the operating cycle?

A is top dead centre, B is the point of inlet port 18 opening, C is where the exhaust valve opens, D is where the inlet port closes, and E is the position at which the exhaust valve closes.

Why does the engine admit more air than needed for combustion?

The quantity of air admitted is much greater than that retained for combustion; the residual gases are at low temperature due to the high expansion ratio, and mixing with atmospheric air produces a mean temperature low enough for the mixture to act as a cooling agent.

What compression ratios does the patent cite for a normal unsupercharged compression ignition engine?

It states the compression ratio is of the order of between 14 and 20:1, with fuel burnt per cycle about 1/20th of the weight of trapped air (air fuel ratio 20:1).

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British Patent 988,378 Page 2 - Chatterton Hyperexpansion 2-Stroke Engine Cycle

Scanned patent specification text page with numbered lines describing a two-stroke engine cycle

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Scanned patent specification page of numbered prose describing a two-stroke engine operating cycle.

AI caption January 2014 · Photo 418 of 465

This is page 2 of British Patent 988,378 (the "Chatterton hyperexpansion" engine patent), describing a 2-stroke compression-ignition engine with an extremely high expansion ratio. The page continues the mechanical description: a piston (20) with rings (21) in a liner (16), connected via gudgeon pin (22) and connecting rod (23) to a crankshaft (25); a cylinder head (26) with an exhaust port (28) closed by a cam-operated poppet valve (30), a central fuel injection nozzle (34), an integral exhaust manifold (35), an exhaust pipe (36) with butterfly valve (37) feeding a separate combustion chamber (38) with flame tube (40) and fuel injector (41), whose gases drive a turbine (45) via a nozzle ring (46) and blade ring (47) on an output shaft (50). It then explains the operating cycle shown in Figure 2, defining compression ratio (v+Vc)/v and expansion ratio (v+Ve)/v, and crank-pin positions A–E for port and valve events. The cycle uses excess inducted air as a cooling agent, with an expansion ratio of the order of 75:1 or higher, and discusses how maximum combustion pressure limits the compression ratio, comparing with conventional unsupercharged compression-ignition engines (compression ratios 14–20:1, air-fuel ratio about 20:1).

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Frequently asked questions

What expansion ratio does the hyperexpansion engine in Patent 988,378 use?: The document states the expansion ratio may be of the order of 75:1 or higher, chosen so cylinder pressure at inlet port opening is below the supply air pressure and exhaust gas temperature is low enough to have a cooling effect.
How are the compression and expansion ratios defined in this patent?: The compression ratio is (v+Vc)/v and the expansion ratio is (v+Ve)/v, where v is the combustion chamber volume at top dead centre, Ve is the piston displacement at the point of inlet port opening, and Vc is the volume swept during the compression period.
What do the crank pin positions A, B, C, D and E represent in the operating cycle?: A is top dead centre, B is the point of inlet port 18 opening, C is where the exhaust valve opens, D is where the inlet port closes, and E is the position at which the exhaust valve closes.
Why does the engine admit more air than needed for combustion?: The quantity of air admitted is much greater than that retained for combustion; the residual gases are at low temperature due to the high expansion ratio, and mixing with atmospheric air produces a mean temperature low enough for the mixture to act as a cooling agent.
What compression ratios does the patent cite for a normal unsupercharged compression ignition engine?: It states the compression ratio is of the order of between 14 and 20:1, with fuel burnt per cycle about 1/20th of the weight of trapped air (air fuel ratio 20:1).