What is in the drum?

[Flightrite]

Higher octane more power output???

[bushcaddy105]

I still use a Ferguson FE-35 petrol/kero tractor from the mid-1950's. The workshop manual gives specs for 3 different fuel versions:- Petrol, Vaporising oil and lamp oil.

Petrol turned out 38.0 BHP on a compression ratio of 6.6 to 1

Vaporising oil 30.5 BHP on CR of 5.0 to 1

Lamp oil 29.0 BHP on CR of 4.3 to 1

I assume that mine is the 5.0 CR and it starts, runs and idles faultlessly on 91 unleaded petrol. I confess that I can't recall having removed the spark plugs in at least 15 years because there's never been the need!

So there's 3 possibilities for what's in the drum.

[facthunter]

OME the calorific value of the fuel is NOT affected by octane rating but kero or avtur in fuel will destroy an aviation motor quick time. Higher octane allows much higher compression ratios which increases volumetric efficiency peak temps and therefore POWER. Tetra Ethyl Lead was introduced specifically in the US in the late 20s for aviation to prevent engines destroying themselves on take off by detonation The highest performance Pistons used avgas 130/ 145 and produced the highest specific HP/Litre ever just after the war where they reached the peak of their development with engines around 3400 Shaft Horse Power.

The low compression kero tractors won't suffer from running on petrol at all. They only used the other stuff because it was cheaper in it's day. Nev

[old man emu]

Higher octane more power output

 

The compression of the fuel/air mixture enables the engine to develop. Engine power is generated when combustion exerts a force on the piston and pushes the piston down the cylinder during the expansion stroke. The higher the piston is in the bore the higher the compression ratio. When combustion begins, more force will be exerted on the piston in a higher compression engine than in a lower compression engine. As compression ratio increases, the piston moves higher in the bore at top dead centre.

 

High compression increases your risk of knocking, which is why high compression engines run high octane fuel. Gases heat up when they’re compressed, so the increased heat density due to compression can lead to the fuel prematurely combusting before the spark plug ignites it. That's "knock". If the combustion occurs before the piston reached TDC, the force of the expanding combustion gases acts against the piston moving to TDC, and that resisting force goes through the head of the piston to the con rod and eventually to the crankshaft bearings. Since the engine is not designed to take forces acting in that direction, damage occurs.

 

So, it's not higher octane = more power, it's more compression = more power, and more compression = higher internal cylinder temperatures, which can lead to premature ignition = a need for higher octane rated fuel.

 

My 1942 bike has a compression ratio of 6:1. It was designed for 74 octane fuel. It happily runs on 91 octane, and for a treat likes a drink of 100LL, but even though the engine has just been reconditioned with new cylinder sleeves, piston and rings, it won't produce any more than 22 HP at 4300 RPM, as it did when it was first fired up on 74 octane petrol.

Edited June 25, 2020 by Admin

[facthunter]

The only way to get high power from low octane fuel is direct injection into the cylinder. High octane fuel is essential on high comp ratio engines or they literally destroy themselves. Nev

[Yenn]

The higher forces on the con rod are a very small part of the problem of low octane fuel pre-igniting. The biggest effect will be felt on the piston crown and even more so on the ring lands.

Low octane fuel works well at wide open throttle if the fuel is injected under pressure at the correct timing before TDC.

[facthunter]

A lot of the older Kero tractor engines are side valve and big displacement. The already low compression ratio is further affected by the restrictive manifolding timing and port shapes so the volumetric efficiency suffers and you only get a % of the static compression as the cylinders are only part filled even with full throttle on the governor on load. 80% would be considered a good figure. Nev

[spacesailor]

Super power Drag racer,s use Alchol, it also runs very cold.

spacesailor