Motorsport Plumbing Systems: System Overview
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System Overview
13.12
| 00:00 | In this section of the course we'll be covering the fuel plumbing system, how it functions, the components involved and what we need to consider for performance in motorsport. |
| 00:10 | Along with the intake air, fuel is the other fluid required for the engine to run and its chemistry can vary significantly. |
| 00:18 | The base level of understanding required in this case is simply that the fuel is mixed with the intake air and is used for the combustion process in an internal combustion engine. |
| 00:29 | In production in motorsport cars, there are various fuels used. |
| 00:32 | The most common being gasoline, also known as petrol, ethanol gasoline blends and diesel. |
| 00:39 | While less commonly, we see LPG and biodiesel, or even methanol or nitromethane in some classes of drag racing. |
| 00:46 | The focus will be on petrol or gasoline based fuels, including ethanol blends, rather than diesel, simply based on them being far more prevalent in performance applications and in motorsport. |
| 00:58 | With that said, a lot of what we will discuss will be relevant for plumbing diesel systems. |
| 01:03 | The fuel we use will be stored on board and that involves a range of considerations and naturally the store will deplete as the fuel is used. |
| 01:12 | The flow and pressure at which we supply the fuel from the tank to the injectors is one of our primary concerns, but we need to ensure that this is done in a safe and reliable manner due to the flammability of the liquid we are working with. |
| 01:26 | It's imperative that the system is free of any leaks as any fuel exposed to high temperatures, sparks or an open flame can ignite. |
| 01:34 | This could happen during operation of the vehicle or after a crash where the driver could be unconscious and incapable of responding. |
| 01:42 | Unfortunately, this has been the cause of many serious incidents over the years. |
| 01:48 | Safety needs to be the top of our list of concerns and carefully considered when designing, fabricating and working on our fuel system. |
| 01:56 | Let's start by discussing the architecture of the fuel system and as always, with the different configurations of vehicles out there, there are some significant differences in the fuel systems that go with them. |
| 02:08 | Again, how each component in the systems works is not the focus of this course, and we're specifically covering the plumbing connecting them but we still need to understand how the system works as a whole. |
| 02:20 | The most common and likely of most interest to us is the fuel plumbing system for modern EFI. |
| 02:26 | So, we'll be looking at a return style plumbing system for port injection. |
| 02:31 | The term return we'll discuss soon alongside the alternative being returnless, but by port injection we mean that there is at least one injector per cylinder that injects fuel into the intake air flow in the port before entering the cylinder. |
| 02:46 | This is much more common than the alternative direct injection where the fuel is injected directly into the cylinder. |
| 02:53 | It makes sense to start with the plumbing that allows us to fill our fuel tank where it's stored, and then we'll discuss how the fuel is conveyed to the rest of the vehicle. |
| 03:02 | In most cases, on the outside of the vehicle we have a fuel filler neck, somewhere we can reach with our filling device, be it a gas station pump or a fuel can. |
| 03:12 | This is a port that's plumbed into the fuel tank, usually with relatively large diameter plumbing to allow for the high flow rate. |
| 03:20 | In factory arrangements, it's common to have a vent from the tank running parallel with the filler neck and they often combine near the filling port. |
| 03:28 | A cap will be used to seal the port when not being filled. |
| 03:32 | Or in motorsport vehicles, we might have a dry brake to help accelerate the filling process during a pit stop, while preventing spillage. |
| 03:40 | Sometimes this will have a separate vent and fill port to help speed things up further. |
| 03:45 | With the fuel in the tank, the next stage is getting it to the engine. |
| 03:49 | Naturally we need a pump to facilitate this movement. |
| 03:52 | In most modern OEM cases, this electric pump will be submerged in the fuel tank and the inlet to the pump will also have a coarse, sock tight filter to remove any relatively large particles from the fuel before it enters the pump to prevent damage and blockages. |
| 04:08 | The pump itself could be external to the tank and in some cases still fed by a smaller intact pump which would usually be referred to as a lift or feed pump. |
| 04:19 | There will also usually be another finer inline filter between the pump and the engine to remove the smaller particles from the fuel. |
| 04:27 | When the fuel level in the tank is low, during a high G turn, acceleration or braking event, it's possible for the fuel to slosh around in the tank and away from the pickup for the pump, leading to inconsistent fuel delivery to the engine, commonly referred to as fuel starvation or surge. |
| 04:45 | This is a common issue for older vehicles that originally had carburettors that require a much lower fuel supply pressure of around 4-8 psi and have been changed to EFI which typically requires over 40 psi. |
| 05:00 | Most modern tanks designed for EFI will have some form of baffling to prevent this issue and keep fuel around the pickup and this is important consideration in tanks designed for performance and motorsport application. |
| 05:14 | Besides solid baffling in the tank, there are also special phones that exist for the same purpose. |
| 05:20 | In any case where the in tank baffling isn't up to the task, another alternative is to use a surge tank. |
| 05:26 | This in most cases is another tank significantly smaller than the main unit which is kept constantly full by a lift pump, as long as there is enough fuel in the main tank of course. |
| 05:37 | A lift or feed pump will maintain the supply of fuel to the surge tank, and the main pumps will draw from the surge tank with no risk of starvation. |
| 05:47 | In some cases there could be multiple pumps or filters plumbed in parallel and then brought together with a wire block at some point depending on the overall fuel requirements for the engine. |
| 05:58 | There are also aftermarket fuel tanks available that have all of this built in with the surge tank and pumps all inside the main tank. |
| 06:07 | On the way to the engine, there's another potential variation, whether the fuel flows through the pressure regulator before or after the fuel rail. |
| 06:15 | Firstly, the fuel pressure regulator does exactly what the name suggests, regulating the pressure of the fuel that the injectors are supplied with. |
| 06:24 | The fuel rail is essentially just a manifold that takes the fuel supply from the tank and distributes it to the injectors. |
| 06:31 | Usually the fuel will flow through the rail first or multiple rails in some cases like V configuration engines with multiple banks or engines with multiple injectors per cylinder and staged injection. |
| 06:44 | After this, the fuel will enter the pressure regulator through one or both of the inlet ports where excess fuel will be plumbed back into the surge tank. |
| 06:53 | It's common for fuel pressure and temperature sensors to be installed on or near the fuel rail to give the ECU a good idea of what the engine is being supplied with, which are important metrics in order to maintain consistent air fuel ratios. |
| 07:08 | Alternatively, the fuel will enter the regulator where the excess fuel will be returned to the surge tank and the pressure regulated fuel will then be supplied to the fuel rails. |
| 07:19 | If we don't have a surge tank, we'll naturally plumb the fuel back to the main tank. |
| 07:24 | But if we do, it's important that the fuel is returned to the surge tank and not the main tank. |
| 07:30 | Otherwise we're essentially emptying the surge tank and plumbing it back to the main tank, which defeats the purpose and will require a much larger lift pump for unnecessary circulation. |
| 07:41 | If we return to the surge tank, then the lift pump only needs to keep up with the engine's fuel volume usage, which is fairly easy as the lift pump is working against relatively little pressure. |
| 07:52 | The main pumps on the other hand do the job of supplying the required fuel volume and pressure, so generally need to be sized bigger. |
| 08:01 | The downside of this system is that the fuel tends to circulate around the surge tank up to the fuel rail and back, which does heat it up. |
| 08:10 | Brushless pumps with speed control that can be mapped against the fuel demands have become a game changer here, but this is getting off track. |
| 08:19 | What's important is that we have the pressure regulator after restrictions like the filter and in the line in general, which could result in pressure drop; and this way we know exactly how much pressure the injectors are getting. |
| 08:32 | It's also important to understand that the pressure set by the regulator will be the same in all parts of the system at least after the restrictions we just mentioned anyway. |
| 08:43 | While we're on the topic of fuel pressure, what's measured at the sensor is the gauge pressure, meaning the pressure relative to atmospheric pressure rather than the absolute pressure which is the gauge pressure plus the atmospheric pressure. |
| 08:57 | The differential pressure across the injector is actually more important than the pressure in the fuel rail alone. |
| 09:04 | This is the pressure difference between the fuel in the inlet of the injector and the pressure at the outlet of the injector, which is usually in the intake manifold. |
| 09:14 | This is a critical part when it comes to EFI tuning and calibration. |
| 09:19 | Put simply, a MAP reference fuel pressure regulator is used to maintain consistent pressure differential across the injector with changing manifold pressures. |
| 09:29 | To achieve this, a pressure signal from the intake manifold is plumbed to the vacuum port on the regulator. |
| 09:36 | This allows the pressure signal to act against the internal diaphragm and spring, which in turn regulates the return flow through the injector in order to maintain a constant pressure differential. |
| 09:48 | The sizing of the fuel lines has a significant effect on the pressure and flow, but we'll be discussing this in more detail in a coming module. |
| 09:56 | Moving on, what we've discussed so far is what's referred to as a return style fuel system, because the surplus fuel supply is returned to the tank for storage. |
| 10:06 | The alternative is of course returnless, and the key difference here is that the pressure regulator is used in the tank after the pump and filter. |
| 10:15 | The result is that we end up with a fixed fuel pressure in this type of fuel system rather than a fixed differential fuel pressure. |
| 10:23 | This in turn means that the differential fuel pressure across the injector is constantly changing depending on the throttle position and manifold pressure. |
| 10:32 | This isn't an issue when it comes to tuning, however the ECU needs to be essentially told what style of fuel system we're using. |
| 10:41 | The main advantage here is that we're able to reduce the amount of plumbing between the tank and the engine. |
| 10:46 | From an OE perspective, this reduces costs and this is one of the main reasons why they've become the norm. |
| 10:53 | In a returnless system, the fuel is in the plumbing system until it's injected, meaning the fuel is exposed to heat for longer. |
| 11:01 | However, the pump is actually cooled by the fuel, meaning the heat it generates from pumping is transferred into the fuel which is going to be worse for a return style system where the fuel is circulating. |
| 11:13 | So, it's a bit of a catch 22 and hard to know what is the lesser of two evils. |
| 11:18 | Before finishing up, it's important to note that gasoline and diesel direct injection systems are plumbed from the tank in a similar manner to what we've already covered, but also feature a mechanical high pressure pump, usually driven off the camshaft. |
| 11:33 | It's unlikely that we'll ever be modifying this away from the factory consideration, so we won't be covering this any further. |
| 11:40 | Carburetted systems are very similar to what we've just covered, but often use a mechanical pump driven from the engine, especially in older factory vehicles. |
| 11:50 | The pressure regulator will usually be before the fuel rail or carburettor and bleed the excess fuel pressure to a return line into the tank from there. |
| 11:59 | The key difference is the pressure that the system will operate at. |
| 12:03 | While EFI will typically require fuel pressure in the range of 45 to 58 psi, a carburettor will usually require around 4 to 8 psi. |
| 12:13 | Before moving on to discuss fuel system materials, let's summarise what we've covered so far. |
| 12:18 | Our engine requires fuel to function and the supply flow rate and pressure are fundamental to the performance of the system. |
| 12:25 | But since fuel is usually highly flammable, safety is always of the utmost concern. |
| 12:31 | With our fuel filler neck plumbed to the tank, we can store our fuel load. |
| 12:36 | This tank is plumbed to the engine fuel injectors through a number of fuel pumps, coarse and fine filters and finally the fuel rails. |
| 12:45 | Surge tanks can also be used here to help prevent fuel surge and starvation issues caused by insufficient baffling in the main tank. |
| 12:54 | The fuel also flows through a pressure regulator, which in the most common arrangement bleeds off excess fuel pressure and returns it to the tank. |
| 13:02 | In a returnless system however, an in tank regulator can be used so we only require a feed line to the engine. |
