Fuel delivery system

A fuel delivery system for an engine, the system comprising:

• a vapour trail detection sensor configured to generate a detection signal indicative of a characteristic of a vapour trail;
• a regulator configured to regulate a volume of a first and a second fuel composition delivered to the engine as resultant fuel composition;
• and
• a controller arranged to undertake a search of trial fuel compositions by controlling the regulator to deliver to the engine a plurality of trial fuel compositions having different ratios of the first and second fuel compositions and to control delivery of a resultant fuel composition to the engine in response to the vapour trail characteristic detection signals for said plurality of trial fuel compositions.

A fuel delivery method for an engine comprising:

• receiving a vapour trail detection signal indicative of a characteristic of a vapour trail produced by the engine;
• regulating a volume of a first and a second fuel composition delivered to the engine as resultant fuel composition;
• and
• undertaking a search of trial fuel compositions by controlling delivery to the engine of a plurality of trial fuel compositions having different ratios of the first and second fuel compositions and
• controlling delivery of a resultant fuel composition to the engine in response to vapour trail characteristic detection signals for said plurality of trial fuel compositions.