The Napier Deltic marine diesel engine, complete with gearbox.
The Deltic end casing with synchronising gears.
A 3d drawing of the Napier engine.

RUDOLPH Diesel’s internal combustion engine has always been on the receiving end of bad press, especially when it comes to emissions and fun but engineers know that the compression ignition engine is superior in terms of efficiency and, therefore, specific power output.

In short, if you want the most grunt for your buck, you have to go diesel even though it isn’t pretty and she smokes a fair bit.

The story of the Napier Deltic is about the quest for power and we are not talking about horsepower here but actual power and dominance over others, we are talking about war.

At the height of World War 2, the British Navy’s Motor Torpedo Boat had developed the habit of eating the dust, or rather, trailing the wake of German torpedo boats and the admiralty wanted the problem fixed, pronto.

The main problem was the engine. While the Germans were already running advanced diesel engines that were powerful enough to twist whale knickers, the British were running petrol engines. They sounded sweet but sweet doesn’t win the war.

What they needed was some serious grunt.

Enter D Napier & Sons, purveyor of quality motor carriages whose products first impressed the subjects of King Edward, and later became quite the aero engine manufacturer during World War 2.

They came up with a diesel engine of 18 pistons arranged in nine cylinders arranged in triangular formation. It must have looked like alien technology then, in fact some people are still convinced that it is.

According to some, the alien link is a two-step process. Let me take you through the theory: Napier had connections with German aero engine manufacturer Junkers and they had been developing aero diesel engines since the 1920s. Some time in the middle of that decade, they came up with the idea of opposing pistons.

Unlike Boxer engines where the opposing pistons are connected by a crankshaft between them, these diesel engines have the pistons connected by the cylinder with crankshafts located at the opposing ends of the bank.

The two pistons would meet in the centre and the resulting compression would trigger combustion and power would be cranked out at the opposing end.

Now you may think that this looks like a long and unnecessarily complex way of arranging piston across from each other, and you are right, but there is a very good reason for doing this.

Not content with developing an opposed piston engine, Junkers wanted it to be more efficient and simpler to maintain; so they made it a two-stroke.

Two-stroke engines are great for cranking out power but they are known to be inefficient because they have no valves and rely on the pistons exposing ports to allow for air coming in and exhaust gases leaving.

Ports are great because there are no moving parts but they are also terrible because there is no way of controlling when they open. Typically they both open at the same time and this usually means none of the exhaust gases can be burnt again because they are displaced by the incoming air that is pushed into the cylinder by the piston’s downward movement.

Poor exhaust scavenging translates into lower engine efficiency and lots of smoke. If only there were a way to vary the opening of the ports and allow for some of the exhaust gas to be re-used.

On motorcycles, this usually means using very precise and complex shaped exhaust chambers to create shockwaves that would kick some of the exhaust gases back into the cylinder but on industrial applications, everything has to be kept simple for cost and maintenance purposes.

Junkers figured that adding an opposing piston so that one piston would take care of the intake port while the other opened the exhaust port was a workable and, perhaps, even an elegant solution.

They could then position the pistons in a way so that the exhaust port would close before the intake port but as most engineers would tell you, you don’t really want to be messing with the port position so what they did was run the pistons slightly out of sync with each other so that they reach top dead centre at different times.

This would result in the ports opening at different times.

Having licensed Junker’s 204 opposed piston diesel engine and lavishing on it the British flair of naming by calling it Culverin, Napier thought of ways to make it even more powerful.

By the way, Culverin is a French word that means musket or small cannon.

As we all know energy cannot be created or destroyed so in order for something to generate power, it has to get energy from somewhere and convert them into the sort of power that is usable.

In the case of engines, the energy comes from the fuel and in order to generate more power, all things being equal, an engine has to burn more fuel.

A turbocharger or supercharger forces more air into the engine and with more air, more fuel can be burnt. The other way is to make the engine run faster; in Formula One the engines used to run at 20,000rpm.

The final way is to add size, the bigger the engine the more fuel it can burn. Some say, there is no substitute for size, some say it’s not the size, it’s what you do with it.

Being British, Napier believes in the second adage.

They decided that if one bank of opposing piston was good, then two could be even better and what if they put together three banks of opposing pistons, with three crankshafts working together?

Think of it as the V6 engines connected at the cylinder head with the three crankshafts connected by gear to synchronise everything. To make it even more powerful, add one turbocharger for each bank of pistons.

That was exactly what they did. Too bad the engine is so complicated that it has taken us the better part of 1,000 words just to get here. But just take a look at the pictures and diagrams and imagine the awe they must have felt when it was first revealed in the 1940s.

These engine found their way into the British Navy and also into British Rail where the Deltic Locomotives broke record after record with such ease that they became legends in their own lifetime.

343 reads

Related Articles

Most Read Stories by