Our first step during the design process was to look to see what had worked in previous years-on our car and other teams' cars. The fuel tank on the 2012 FSAE car had an issue of fuel starvation. This is essentially when the fuel sloshes in the gas tank and the fuel pump can not correctly pump it. One of the reasons for this was due to the fuel tank being too wide. This allowed to fuel to move back and forth a large amount during cornering. This was one issue we needed to resolve.
The next step we took was to look at other teams gas tanks to get ideas. These were some of the gas tanks we looked at:
These tanks incorporate a fuel catching system to avoid the fuel starvation. The first picture shows an aluminum tank with a step down to catch the fuel. The second tank looks more like an fuel bladder in an aluminum shell.
Tank Design
The next step in our design process was to develop an approximate shape we wanted for the fuel tank. Using Solidworks, we analyzed the model of the 2013 FSAE chassis in order to find approximately where we wanted the tank to go in the car. The tank, since it is a dynamic weight instead of a static weight, needed to be mounted close to the center of gravity as possible. Also, the rules dictate it must be enclosed within the car. The previous tank was mounted towards the right of the frame, which was also a possibility. So, we looked at the 3D model of the frame.
The plate running through the frame represents the firewall between the gas tank and engine and the driver. The fuel tank needs to be behind that and centered. Next, measurements were taken.
After observing these measurements, we decided on a shape that was tall and with a slanted front to be as close to the fire wall as possible. We went with a shape like this:
In order to create this shape, we used 3D sketching in Solidworks and observed how it fit in the car.
We found that this tank appeared to fit very well in the car, tight to the firewall, and utilizes as much vertical room as possible which will allow for better packaging within the car. The tank also had a volume of 347 cubic inches, or approximately 1.502 gallons. Since this volume and size appeared to be exactly what we wanted, we continued with the design of our tank.
Fill Plate and Neck Design
The next aspect of the fuel system that needed to be designed is the way for the fuel to be moved in and out of the tank. The aspects we needed to include were a filler neck, an outlet, a vent, and a return. The filler neck is used in order to fill the gas tank. It has to be 1.5" in diameter and easily accessible for filling. The outlet is a hole used to draw fuel out of the tank. The vent is to vent air in and out of the tank in order to keep the tank from becoming pressurized and exploding. Last, the return is another hole for the excess gas to be returned to the tank after it has passed though the fuel pressure regulator mounted on the fuel rail.
Our initial design had a plate in the top right corner of the tank, which would house the vent, return, and filler neck. The outlet, however, would be on the bottom of the tank, in order to have the ability to pull gas from the lowest point in the tank.
The next step was to place the return, filler neck, vent and outlet into the model to observe how they fit in the chassis.
At this stage we realized we had made an error when placing the outlet on the bottom of the tank. Since it was on the bottom, the fittings to connect to a gas line would either have to go underneath the frame of the car, which could potentially be dangerous, or the gas tank would have to be raised, which would cause issues for mounting and raise the Center of Gravity for the car. So, in order to fix this, we decided to place the outlet on back of the tank, still near the bottom. The back was chosen so that under acceleration the fuel pump would receive gas.
Also, we decided to change where the filler neck exited the frame. This was in order to get rid of the long horizontal piece of aluminum tubing. On last year's gas tank, this caused the sight tube to not work correctly. This design is shown below.
Once again, we decided to change the design in order to be more efficient. Where the filler neck exits the frame currently it would have been impossible to actually fill with gasoline. In order to fix this, we dropped the filler neck down below the node. However, it is still not horizontal, so we believe it will not cause the sight tube any issue. The final design is shown below with the mounting system as well.
