Adjusting a fuel on-board a vehicle

A method for separating a fuel on-board a vehicle, comprising:

• separating, with a first stage fuel separator, a heated fuel stream into a vapor stream and a first liquid stream based on a volatility of the fuel stream, the vapor stream defined by a first auto-ignition characteristic value and the first liquid stream defined by a second auto-ignition characteristic value, the second auto-ignition characteristic value greater than the first auto-ignition characteristic value;
• separating, with a second stage fuel separator arranged in series with and downstream of the first stage fuel separator, the vapor stream into an oxygenate stream and a compound stream;
• directing the oxygenate stream from the second stage fuel separator to combine with the first liquid stream;
• directing the combined stream to a secondary heat exchanger;
• supplying an unheated fuel stream and the vapor stream from the first stage fuel separator to a primary heat exchanger;
• transferring heat from the vapor stream to the unheated fuel stream to heat the unheated fuel stream;
• circulating the heated fuel stream through a variable orifice fluidly coupled directly between the primary heat exchanger and the first stage fuel separator;
• controlling the variable orifice to adjust a pressure of the heated fuel stream between the primary heat exchanger and the first stage fuel separator with the variable orifice so that the first auto-ignition characteristic value of the vapor stream meets a desired vapor stream auto-ignition characteristic value, and the second auto-ignition characteristic value of the first liquid stream meets a desired liquid stream auto-ignition characteristic value;
• controlling at least one of the first stage fuel separator or the variable orifice to vary a volumetric flow rate of at least one of the heated fuel stream, the vapor stream, or the first liquid stream;
• supplying the heated fuel stream to the first stage fuel separator;
• and
• supplying a second liquid stream defined by the first auto-ignition characteristic value from the primary heat exchanger to a fractional fuel tank.

A vehicle system, comprising

• a vehicle;
• a fuel-powered internal combustion engine mounted in the vehicle;
• an on-board fuel separation system, comprising:
• a first stage fuel separator configured to receive a fuel stored in the vehicle and separate the fuel, based on a volatility of the fuel stream, into a vapor stream defined by a first auto-ignition characteristic value and a first liquid stream defined by a second auto-ignition characteristic value, the second auto-ignition characteristic value greater than the first auto-ignition characteristic value;
• a second stage fuel separator arranged in series with and downstream of the first stage fuel separator and configured to separate the vapor stream into an oxygenate stream and a compound stream, the second stage fuel separator further configured to direct the oxygenate stream to combine with the first liquid stream, and to direct the combined stream to a secondary heat exchanger;
• a primary heat exchanger fluidly coupled between a fuel input of the fuel and the first stage fuel separator, the primary heat exchanger configured to transfer heat from the vapor stream to the fuel, and output a heated fuel stream to the first stage fuel separator and a second liquid stream defined by the first auto-ignition characteristic value;
• and
• a variable orifice fluidly coupled directly between the primary heat exchanger and the first stage fuel separator to receive the heated fuel stream and adjust a pressure of the heated fuel stream that enters the first stage fuel separator;
• a first fuel tank fluidly coupled between the engine and the first stage fuel separator to store the first liquid stream output from the first stage fuel separator;
• a second fuel tank fluidly coupled between the engine and the secondary heat exchanger to store the second liquid stream output from the secondary heat exchanger;
• and
• a controller operatively coupled to control at least one of the first stage fuel separator or the variable orifice to vary a volumetric flow rate of at least one of the heated fuel stream, the vapor stream, or the first liquid stream, and adjust the pressure of the heated fuel stream so that the first auto-ignition characteristic value of the vapor stream meets a desired vapor stream auto-ignition characteristic value, and the second auto-ignition characteristic value of the first liquid stream meets a desired liquid stream auto-ignition characteristic value.