No, it's not what you think - although the smoke is diesel smoke.

This week, for the first time in fifteen or so years, the Napier T9 29 Deltic engine which is at the heart of the project was warm again. Not through internal combustion but through external combustion. We bought two Stroco heaters years ago and the time was right for getting them working, one is little more than a collection of spares but the other one worked with minimal effort. Connected to a 24v power supply and with a domestic heating pump circulating the water the heater raised the temperature of the engine by 35 degrees or so in a little over 20 minutes. The central heating pump isn't up to the job so it's been replaced.

Of note in the photo below, the heater (bottom left, almost obscured in its own exhaust), the connections to the engine (complete with isolating cocks), the make-up pipe disappearing off to the top right. The hardboard cover is to protect the engine exhaust.

This photo was taken almost immediately after the heater was started, the smoke cleared quickly and was little more than a grey haze once the combustion chamber had warmed up.