Stupid Question but I want to get an answer

Yes, but as pointed out by you, Sooraj was Enfield/Bullet itself.  It was seen in rural areas of various states.

I think, other than Enfield/Bullet/Sooraj, no other bike came with diesel engine.

Sooraj was based on an Enfield frame and fitted with a Greaves diesel engine, but the vehicle was built by a company called Sooraj Automobiles LImited in Saharanpur, UP.

Here's a Sooraj Diesel ad:

After Sooraj did this with reasonable success, Royal Enfield woke up and decided to do exactly the same thing by themselves.  So they brought out the Diesel Enfield which was essentially the same thing, but with a full Enfield frame and body parts.  It was also SLIGHTLY better built than the Sooraj - at the very least fewer body parts fell off while the vehicle was running.

They also sold this abroad under the name of Enfield Robin, but with a slightly bigger diesel (still a pumpset, though).  It became a joke abroad.

There have been military motorcycles powered by diesel engines in the past, but the first real commercial-scale diesel motorcycle can be seen here:

http://www.dieselmotorcycle.co.uk/ 

The engine is very interesting - 800cc Common Rail diesel developing 45 bhp and 100 nm.  Sounds like the sort of engine that could power the Nano. 

Thanks Steeroid.  I was under the impression that Sooraj was brand of Enfield itself.  I vaguely remembered Sooraj Automobiles but for its 3-wheelers. 

I now learn that the Company produced 3-wheelers only much later - first they produced Sooraj bike.  Sooraj motorcycle happens to be 1st commercially produced diesel motorcyle in the World.

Thanks again.

Steeroid:

Thats a gud one man... The quote looks cool

"A blend of Power & Economy"

Cheers,
Sai