Ted Bell wrote:

If I've read it right a diesel compresses the air to a very great
extent. The compression heats the air so much that fuel self-ignites
when injected into the hot air. Even if it's very cold it's my
understanding the compressed air is still hot enough to ignite the fuel.
So it seems to me if the fuel doesn't ignite maybe it's because it's so
cold and thick that the injectors don't spray it in properly.

It is more common, particularly on engines well past their youth, that
compression is not as good as it should be. The result is that the
compressed air doesn't get hot enough quickly enough at low revs in
a cold engine block. This seems a likelier scenario than the fuel
being too viscous at low temperature to disperse properly.

Maybe just
dribbles of larger droplets that are reluctant to burn. So heating the
injectors seems like it would take care of that problem. Sort of the
same principle that a pressure diesel stove uses to pre-heat the fuel.
Meths don't burn all that hot so although it might blacken the paint I
can't see where it would damage the injector. I think I'll give it a go.

Many engines are fitted with electric glow-plug preheaters. I don't think
they heat the injectors, but part of the combustion chamber. On some
engines, electric heater coils are located within the air intake. This
is an easy option to retro-fit (unlike glowplugs which really need to
be designed in from the start), and Bukh, for instance, offer this option
and I can vouch for how well it works. They basically preheat the air, so
that it's already warmer before it gets heated by being compressed. The
result is that the compression heats the air up to an even higher
temperature, making it more likely that the engine will fire sooner.

I would recommend that if you want to have a go, it would be a better idea
to heat up the air intake than the injectors.