Tractor vapourisin ile

**Tractor vaporising oil** (or **TVO**) is a fuel for petrol-paraffin ingines. In the United Kinrick an Australie, efter the Seicont Warld War, it wis commonly uised for tractors until diesel ingines became commonplace. In Australian Inglis it wis kent as **power kerosene**.

## History
TVO existit for at least fifteen years afore it became widely uised. A 1920 publication mentions it as a product o Breetish Petroleum. But it wis nae until the late 1930s that it first became widely uised. The post war Ferguson TE20 tractor, a carefully researched an near-ideal tractor for uise on Breetish farms, wis designed aroond a petrol (gasoline) ingine, the Standard inline-fower. Awtho thare wis a campaign for the reintroduction o agricultural Road Duty (tax)-free petrol, which haed been curtailed during the war, this wis nae forthcoming. Perkins Engines supplied some conversions intae diesel ingines which coud uise untaxed reid diesel.

On the early Fordson model N, the tap which changed ower frae petrol tae TVO wis merked G for gasoline an K for kerosene, reflecting that thir tractors haed thair design origin in the USA. In the UK tractor vaporising oil wis uisually cried TVO.

## Octane rating
As a substitute for petrol, TVO wis developed. Paraffin (kerosene) wis commonly uised as a domestic heating fuel an wis untaxed. Paraffin haes a law octane rating an wad damage an ingine biggit for petrol. The manufacture o paraffin involves the removal o aromatic hydrocarbons frae what is nou sauld as heating oil. Thir aromatics hae an octane rating, sae adding some o that otherwise waste product material back in a controlled manner intae paraffin gae TVO. The resultin octane rating o TVO wis somewhere atween 55 an 70.

; Octane ratings o various fuels

; Octane ratings o petrol/heating oil mixtures

* pbv = pairts bi volume

The words paraffin an kerosene are eften uised interchangeably but the tables suggest that this is incorrect acause thay hae different octane ratings. Houiver, kerosene an heating oil hae seemilar octane ratings. Paraffin, kerosene an petrol (gasoline) are aw rather loosely defined. For ensaumple, gasoline mey hae an octane rating atween 95 an 102.

## Ingine modifications

### Compression ratio
Because TVO haes a lawer octane rating than petrol, the ingine needs a lawer compression ratio. On the TVO version o the Ferguson TE20 tractor, the cylinder heid wis re-designed tae reduce the compression ratio tae 4.5:1.  This reduced the power output, sae the cylinder bore wis increased tae 85&nbsp;mm tae restore the power. The petrol version haed a compression ratio o 5.77:1 an a cylinder bore o 80&nbsp;mm on early versions..

### Vaporiser
In practice TVO haed maist o the properties o paraffin, includin the need for heating tae encourage vapourisation. As a result, the exhaust an inlet manifolds war adapted sae that mair heat frae the umwhile warmed the latter. Sic a setup wis cried a vaporiser. Tae get the tractor tae stairt frae cauld, a smaw seicont fuel tank wis added that contained petrol. The tractor wis stairtit on the expensive petrol, then – ance the ingine wis warm – the fuel supply switched ower tae TVO or paraffin. Sae lang as the ingine wis wirkin haurd, as when ploughing or pulling a load, the TVO wad burn well. Unner licht conditions, sic as travelling unloaded on the highway, the ingine wis better on petrol.

### Radiator blind
Some tractor designs included a radiator "blind" that wad restrict the flow o air ower the radiator which led tae the ingine running hetter, which coud help wi stairtin. If the radiator blind wis left shut, tho, thare wis a risk o ingine damage, especially in warm wather.

## Terminology
The phrase petrol-paraffin ingine is eften uised tae describe an ingine that uses TVO. This can be interpreted aither as

:* the use of the two fuels, starting on petrol then switching to the paraffin-based TVO
:* the use of a mixture of petrol and paraffin as a substitute for the proper TVO

## Supply
TVO wis withdrawn frae sale bi UK suppliers in 1974 but haes been re-introduced bi at least ane supplier (Rye Oil Ltd). An approximation tae the correct specification can be made frae petrol an heating oil (burning oil). In the UK thare is an exception that permits the uise o rebated kerosene an fuel oils in vintage vehicles.

## Notes and references