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/ Categories: Archive, oil-system

Oil tanks

oil-pumpsWhere regulations allow, most racecars run a dry-sump oil system, with the engine lubricant scavenged from the crankcase and stored in an external tank. This allows for a higher degree of oil control, a reduction in the possibility of oil surge and starvation, better de-aeration of the oil and, where applicable, a reduction in installation height thanks to the elimination of the sump pan.

The design of the oil storage tank is of vital importance to the efficiency of the system, with the tank required to perform a number of tasks beyond simply holding oil. There are several key factors that dictate the design of an oil tank, relating to the specific requirement of the overall vehicle package.

As oil is pumped around the engine it is subject to an extreme degree of agitation, both when running through bearings and as it travels back to the bottom of the crankcase. The crankshaft, con rods and other reciprocating parts churn the oil into a foam-like consistency, of greater volume than the original fluid. It is for this reason that the scavenge stages of an oil pump are generally of a greater size or number than the pressure stages, in order to account for this greater volume.

With the oil removed from the engine, it is then the task of the storage tank to separate the oil-gas mixture back to a substance that can be used as a reliable lubricant. This is achieved by controlling the flow of oil into the tank through the orientation of the inlet and, usually, a series of baffles. The oil is generally fed into the tank in a fashion that will encourage it to 'spiral' into the main oil pool, with a number of flat plates used to slow the oil down to allow more time for it to de-aerate. The plates also act as baffles to restrict vertical movement of the oil under high g-loads, and can be complemented with vertical plates to control lateral slosh.

In high-end applications, such as Formula One and Sports Prototypes, extensive CFD simulation is undertaken to establish how the oil will behave in the tank. This is essential to allow for the minimum quantity of oil to be run without compromising flow to the engine, with every extra litre contributing to the overall weight of the vehicle.


oil-pumps-arrows-oil-tank

Constructing a tank in the way described above is simple when there is space to package a regular cylindrical unit, but matters become more complex when installation space is at a premium. This is the case with many top-level single-seat racecars, and current Formula One technology is a case in point.


In a current-generation Formula One car, the tank is generally housed on the front of the engine in order to optimise both space and weight distribution. This does not allow for a simple cylinder, however, and the tank's shape is dictated by the space between the engine and the safety cell. The result is a tank that requires many more compartments and baffles to control the oil flow effectively.

Most high-performance race engines run at a negative crankcase pressure, with the dry-sump pump capable of creating a considerable level of vacuum. The oil tank therefore needs sufficient venting to allow the gaseous mixture evacuated from the engine to escape, otherwise the efficiency of the pump is compromised.

From this brief overview it can be seen that oil tank design is one of the key components in an effective oil system, with the overall vehicle package and engine requirements dictating the end product. As with any race machine, every component needs to be optimised, and the humble oil tank is no exception.

Fig. 1 - This fabricated tank on an Arrows Formula One car shows the level of complexity in a high-performance oil tank (Courtesy of Concept Racing)

Written by Lawrence Butcher

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