BRIEF

A Naturally aspirated engine draws in air and fuel into its combustion chamber, compresses, ignites and exhausts the resulting gases away. Traditionally, superchargers are belt driven from the engine, sapping around 20% of the engines power output to drive a compressor. This compressor increases the intake air's pressure, meaning more ends up in the cylinders. To keep the air/fuel ratio efficient, the engine adds more fuel to the mix, which has the result of increasing engine power. The compressor allows the engine to make more power than it originally did, creating a net gain across the rev range.

Simply put, a purely mechanical supercharger on a 100HP engine may "cost" 20HP to run, but it may generate 40HP. This has the net effect of a +20HP increase in engine power, a respectable increase.

The main advantage of an electric supercharger is that there is no sacrifice of engine power to run the compressor. Instead, energy stored in batteries provide the boost. Using the setup above could result in a net gain of +40HP, a massive spike in performance.

The sacrifice instead is that the extra power is now in limited supply. Batteries can only store so much energy, and driving a compressor, as stated above, could cost as much as 20HP, a whopping ~15kW of electrical energy.

But it is possible! The roots-type supercharger below is mounted to a gearbox and three starter motors. An unrelated dyno graph on the right shows a different electric supercharger's performance.

The dyno graph on the right has an interesting characteristic that is to be expected with an electric supercharger: The torque curve decreases over the rev range. This is because the compressor is spinning independently of the engine, moving the same volume of air across the rev range. Therefore it produces the biggest gains when the engine is at its lowest revs, as the engine needs the least.

CHALLENGES

This presents me with a number of challenges:

1. I must choose a suitable compressor
2. I must choose a suitable motor to drive that compressor
3. I must choose a power supply for that motor
4. I must be able to control that power so I can use it when needed.
5. Research into the topic areas where my knowledge is lacking.

RESEARCH

At this point in time, I have limited knowledge of compressors; moderate knowledge of motors and power supplies; good knowledge of control systems. I will need to focus my research to learn about the topics i am least confident with, as I could make the biggest failures there.

To conduct my research I will be creating a research log and mock research papers. In the past, I have written essay-style papers which I find helps me consolidate my learning and can be used as guides for later on. I am not a university student, and I have limited time, so these papers will be short.

To fill these papers, I will be using lots of google-fu, with the odd email to others that have made electric superchargers.

PROJECT GOALS

I will carry out the research above as progress towards my three main goals:

1. Develop a functional prototype
2. Performance test the prototype
3. Present everything on Hackaday.io

This project probably wont change the world for the better, but it should hopefully make my car quicker in a straight line - and which is really more important?

TIMELINE

I will be starting college again in September, where I would like to use this project as evidence towards my qualification. This should give me from now up until January 2017 to complete the project.

Having worked on prototyping projects in the past, I know that this is not a long time. Seven months goes quickly, and I expect the designing to be an iterative process spanning the bulk of my time.

It is my opinion that designing Gantt charts, setting milestones, having deadlines etc is less fun than just getting on with it. This project is entirely self-driven and my motivation is key to its success. I will carry out research until I am happy, then design with what I have.
Any mistakes I make will be investigated, and I will re-design to improve.

Regardless of what i said before, I would like to have a working prototype fitted to my car by Christmas, to show off. If it only exists on paper by then, I will be disappointed, but the work will still be usable for my college project.