Re: air - fuel ratio

Mortimer wrote:
> "Nate Nagel" <njnagel@[EMAIL PROTECTED]
> wrote in message 
> news:fvuo59119s3@[EMAIL PROTECTED]
>>> If you believe in those calculations, then why
>>> not put diesel in your car? That would give you the best mileage.
Right?
>> Oddly enough, it does.
> 
> I've always wondered: is it the higher compression ratio or the
different 
> fuel which gives diesels their greater fuel economy and their greater 
> low-end torque. Or a combination of the two? 
> 
> 
Diesels benefits from three main factors:

1: Higher mechanical compression ratio. Cycle efficiency is a function 
of expansion ratio. This is one of the biggest reasons Diesel have 
higher torque.

2: Unthrottled operation. In the Diesel cycle load is controlled by fuel 
alone. This reduces gas pumping losses incurred during the 
intake/exhaust strokes. In future Diesels this may fade somewhat as 
throttling is being used to facilitate achieving the EGR levels needed 
to meet oxides of nitrogen regulations.

3: Fuel heating value. Diesel fuel contains around 10% more energy per 
gallon than gasoline. Diesel fuel is formulated to promote autoignition, 
the Diesel cycle ignition method. The metric for this is called the 
cetane rating. The higher the cetane rating the lower the octane rating. 
For Diesel engines high cetane fuel is desirable. This is obviously 
undesirable in a spark ignition engine.