On-board fuel adjustment by molecular separation

An on-board fuel separation system, comprising:

• a supply fuel tank configured to store an input fuel stream;
• a first heat exchanger fluidly coupled to the supply fuel tank and configured to receive the input fuel stream from the supply fuel tank and heat the input fuel stream to deliver to a fuel separator, the first heat exchanger fluidly coupled to the fuel separator to receive a first fractional fuel stream from the fuel separator to transfer heat, in the first heat exchanger, from the first fractional fuel stream to the input fuel stream;
• a second heat exchanger fluidly coupled in series between the first heat exchanger and the fuel separator and configured to receive the input fuel stream from the first heat exchanger and further heat the input fuel stream to deliver to the fuel separator, the second heat exchanger fluidly coupled to the fuel separator to receive a second fractional fuel stream from the fuel separator to transfer heat, in the second heat exchanger, from the second fractional fuel stream to the input fuel stream;
• the fuel separator fluidly coupled to the second heat exchanger and configured to separate the input fuel stream into the first fractional fuel stream and a second fractional fuel stream, the fuel separator comprising a membrane that comprises a plurality of pores sized based on a molecular size of one or more components of the first fractional fuel stream, the membrane comprising a molecular sieve or nanofilter;
• a first fractional fuel tank fluidly coupled to the fuel separator to receive the first fractional fuel stream passed through the membrane, the first fractional fuel stream defined by a first auto-ignition characteristic value;
• and
• a second fractional fuel tank coupled to the fuel separator to receive the second fractional fuel stream from the fuel separator, the second fractional fuel stream defined by a second auto-ignition characteristic value that is different than the first auto-ignition characteristic value.

A vehicle system, comprising

• a vehicle;
• a fuel-powered internal combustion engine mounted in the vehicle;
• a supply fuel tank;
• an on-board fuel separation system comprising:
• a first heat exchanger fluidly coupled to the supply fuel tank and configured to receive an input fuel stream from the supply fuel tank and heat the input fuel stream to deliver to a fuel separator, the first heat exchanger fluidly coupled to the fuel separator to receive a first fractional fuel stream from the fuel separator to transfer heat, in the first heat exchanger, from the first fractional fuel stream to the input fuel stream;
• a second heat exchanger fluidly coupled in series between the first heat exchanger and the fuel separator and configured to receive the input fuel stream from the first heat exchanger and further heat the input fuel stream to deliver to the fuel separator, the second heat exchanger fluidly coupled to the fuel separator to receive a second fractional fuel stream from the fuel separator to transfer heat, in the second heat exchanger, from the second fractional fuel stream to the input fuel stream;
• and
• the fuel separator fluidly coupled to the second heat exchanger and configured to separate the input fuel stream into the first fractional fuel stream and the second fractional fuel stream, the fuel separator comprising a membrane that comprises a plurality of pores sized based on a molecular diameter of one or more components of the first fractional fuel stream, the membrane comprising a molecular sieve or nanofilter;
• a first fuel tank fluidly coupled to the fuel separator to receive the first fractional fuel stream passed through the membrane, the first fractional fuel stream defined by a first auto-ignition characteristic value;
• and
• a second fuel tank coupled to the fuel separator to receive the second fractional fuel stream from the fuel separator, the second fractional fuel stream defined by a second auto-ignition characteristic value that is different than the first auto-ignition characteristic value.