29 April 2013
Technical feature: F1 fuel systems
In the latest in a series of technical insights relating to its F1 powerplant, Renault Sport explains the intricacies of the fuel system...
This year, the final year of its RS27 powerplant, the Renault Sport operation explains each of the key systems of the V8 engine in detail.
The subject this time is the fuel system, a key component at the boundary between the chassis and the engine teams, with the chassis team designing and operating the fuel cell and lift pumps and collector, and the engine team taking responsibility for the main fuel pump, filters and injectors.
The task of the engine's fuel system is to recover the fuel from the fuel tank and deliver it to the engine where it is sprayed into the trumpets to mix with air on the way into the cylinder, where the fuel-air mix is ignited to generate torque. The fuel must be delivered to the injectors at the correct pressure so the quantity injected can be accurately metered, so the fuel system is designed to recover fuel from the tank and increase and regulate this pressure by means of a sophisticated mechanical pump.
The fuel system starts with the fuel cell, better known to the layman as the 'tank', which is located within the monocoque behind the driver, but in front of the engine. It is a large leak proof flexible bladder made of military grade ballistics material to contain all the fuel necessary for the car during a race - approximately 160kg or 230 litres. The hoses feeding fuel to the engine are equipped with dry-break frangible couplings so, if the engine and chassis become separated in an accident, fuel cannot leak from the broken hose, which would create an obvious fire risk as per the accidents of the 1970s.
The fuel inside the bladder is subject to lateral and longitudinal g-forces due to cornering, acceleration and braking. The fuel therefore sloshes around the tank, moving from side to side and back and forth. As a result, it can be tricky to recover the fuel as it moves around in the tank, particularly at low level - imagine drinking with a straw from water bumping around on a tray compared with drinking the same water with a straw in a bottle!
The tank therefore contains a number of low-pressure electrically powered 'lift pumps', typically three or four of them, positioned to suck up fuel from the tank corners. Filters at the entry to these pumps protect them from damage that may be caused by impurities that may have entered the fuel cell. The lift pumps deliver to a smaller vessel within the fuel cell known as a 'collector', which typically has a capacity of 2.5kg or three litres.
The collector is pressurised by the lift pumps, and contains enough fuel to feed the main pump continuously, even if supply from lift pumps becomes intermittent at low fuel levels, particularly bearing in mind that an engine running at full revs will need up to 3.5 litre of fuel every minute. The collector looks like an upside down soda bottle - that is, tall and slim - to ensure the fuel supply is constant.
The next stage is for the collector to deliver fuel to a mechanically-driven fuel pump that in turn delivers fuel to the injectors. In fact, the role of the main pump could be compared to a domestic jet washer operated by a push button which takes tap water at low pressure and delivers it at much higher pressure to the spray lance when required, but when the button is not pushed nothing is delivered.
The pump is entirely mechanical and must be protected by a fine filter at the entry. This pump delivers fuel flow fundamentally proportional to engine RPM. The fuel consumed by the engine is also approximately proportional to RPM at full throttle, but at closed throttle, the engine uses no fuel. To match the fuel supplied to the fuel required, the main pump has a variable displacement mechanism actuated by a sophisticated pressure regulating device.
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