Kaine's Jacket

[maersk]

The internal combustion engine is only about 29% efficient. Diesel is much more efficient at about 32%. OK still pretty dire in the absolute scheme of things.
The petrol engine requires a large water jacket around the engine to keep it cool as a lot of the energy from the fuel is wasted as excess heat.
As diesels are more efficient (more of the fuel is converted in to 'go' less into wasted heat)the water jacket can be much smaller. As it still needs to have a maximum calculated volume to keep the engine cool at times of peak use, idle and low rev use mean that technically the jacket is too large and it cools down. Or it takes an age to heat up. Coventry climax racing engines (and their Imp derivatives) suffered a similar long heat up period because of their then radical all aluminium construction.
The auxiliary heater is there to artificially heat the system. The arbitary 6 degrees is calculated as being the lowest temps we driver people can put up with a cool heater. Actually as there is a climate control compressor in the system it transfers heat during the warm up period. Another reason for leaving it 'on' all the time.
Hope this is not as clear as mud.
Incidentally my racing Imps revved to in excess of 10k. They were a wonderful engine, very effective in a Clan Crusader or Davrian. Bu that is another story.

 

[John Disdale]

Maersk,

Thanks for the better explanation. You highlight that the diesel engine does not waste its energy to such a degree as the petrol engine, but is it not also the case that because the diesel engine is so low revving that it generates less frictional heat ? This I specifically mention when I find it quite unbelievable that often I am cruising along at only 1,200 rpm.

Maybe it’s a daft question, but is there a “best” technique for getting the engine hot more quickly –naturally in a safe manner ?

Regards
John Disdale

 

[Harps]

JD - surely you just have to take your clothes off in front of your Golf to make it hot!

 

[Kaine]

Cheers Maersk. Muddy water is just started to settle and clear -

Kaine

 

[maersk]

No quick method other than keeping the air con compressor on.
Any frictional improvement is negated by the need for improved piston sealing due to the considerably higher combustion pressures (about 21:1 as opposed to a 'good' petrol of 10:1 or so)
The cetane rating (diesel equivalent of octane)is significantly higher for diesel. Therefore more energy is contained in a given volume of the fuel. However, diesel has a reluctance to burn despite its self combustion in the compressed and therefore hot atmosphere of the combustion chamber. Beacause of this reluctance, it takes longer to burn, consequently there is a limit to the speed at which the engine runs. Hence lower engine speed.

 

[maersk]

But, by generating more torque due to the efficiency of combustion (partly due to high combution pressures - compression ratio) the diesel can 'pull' a higher final gear ratio.
Its the torque that does it.
That is why diesels are so satisfying to drive in modern give or take conditions. [^]
Conversely that is why Hondas in general and their VTECs in particular are a pain in the ass unless you are on your favourite -empty - road or a track. The high revving high power engine is a delight but max torque is lighter than a diesel and is generated (much) higher up the rev range so you have to screw the nuts off it for it to really go. Hondas do really go though.
Most bike engines rev to astronomical levels and are a total hoot to ride. But thats another story.
Back to the 1100cc race Imp scenario then.