Engine Optimisation

In the early 1960’s my mother ran a very nice Mercedes 230SL, one of the very first in the area and it may have been the foundation of my interest in cars.

Mercedes 230SL

It had a 2.3 litre straight 6 cylinder engine with Bosch mechanical fuel injection, one of the very early production cars to have injection rather than carburettors. The W113 model range was also one of the first to have separate heating controls for passenger and driver. Radial tyres and crumple zones front and rear made for an advanced vehicle for the 60’s

The car was very well engineered and was a joy to drive but every couple of months (according to Mother) it would start to misbehave slightly, reluctant to start, the occasional misfire and not revving smoothly. Of course the local Mercedes garage was always quick to respond, sending a mechanic to sort out the issue and leaving a large bill in return.

After several of these episodes (and bills too) the mechanic confided to mother that the problem was the fuel injection system ‘gumming’ up. This was because the car was only used for short trips. His preferred solution was to drive to the nearby A1 and thrash the car in 2nd gear for about 10 miles, a callout job he enjoyed!

DPF’s – A modern problem.

These days a different problem afflicts modern engines, particularly diesels, the DPF – Diesel Particulate Filter.

DPF - Diesel Particulate Filter

A DPF is a filter that captures and stores exhaust soot (some refer to them as soot traps) in order to reduce emissions from diesel cars.

But because they only have a finite capacity, this trapped soot periodically has to be emptied or ‘burned off’ to regenerate the DPF.

This regeneration process cleanly burns off the excess soot deposited in the filter, reducing the harmful exhaust emission and helps to prevent the tell-tale black smoke you used to see from diesel vehicles, particularly when accelerating.

I have recently been a passenger in a small diesel van that was used for very short journeys and it seemed to have a permanent warning light.

“DPF Full – Please take an extended drive”

Plus ca change, plus c’est la meme chose….

Petrol or Diesel?

Accurate figures are hard to come by, but my best estimate is that diesel cars account for around 50% of the car market at present and that share is increasing. Some time ago I read an article about the contents of a barrel of oil and the figures are as follows:

Product Gallons Percentage
gasoline 19.5 44.12%
distillate fuel oil (Includes home heating oil and diesel fuel) 9.2 20.81%
kerosene-type jet fuel 4.1 9.28%
residual fuel oil (Heavy oils used as fuels in industry,
marine transportation and for electric power generation)
2.3 5.20%
liquefied refinery gasses 1.9 4.30%
still gas 1.9 4.30%
coke 1.8 4.07%
asphalt and road oil 1.3 2.94%
petrochemical feedstocks 1.2 2.71%
lubricants 0.5 1.13%
kerosene 0.2 0.45%
other 0.3 0.68%

Discounting the differences in fuel consumption between the two engine types I think that there is a glaring anomaly here. We are producing twice as much petrol as diesel for the same number of vehicles of each type, so the question is: How is it accounted for, where is all the surplus petrol going?

I understand that there are far too many variables to grapple with, and that a barrel of oil varies in consistency and content depending on its geographical area of production but I don’t understand why there is no information available for the discrepancies. Note also that the “Distillate Fuel Oil” covers heating oils too, so there is a bigger difference.

Over time I have remarked upon this to various people but no credible answer has been given…. Can you help?