Modern cars are blessed with numerous sensors for the assessment of engine function. This sensitivity gives the engine management system the ability to adapt to a wide range of atmospheric and fuel and engine conditions. This exceptional versatility allows for increased fuel economy and power while ensuring longer engine life. In addition to this it allows the engine to take full advantage of fuels with different properties (octane or RON generally). What I would like is for the computer to provide me with a simple readout showing the overall quality of the fuel currently being used and the impact that fuel is having on performance. Since the fuel requirements of every car are different and the market place provides near nil useful information about fuel formulation it would be pleasant if my car would go ahead and tell me what fuel provides maximal performance and fuel economy. The car could give a simple Five Star rating to the novice user and provide more in-depth information (maximum safe boost level, specific output, fuel density) to the more experienced driving enthusiast. If my on-board computer can practically tell me when to stop and pee, why can't it tell me what flavor of fuel the car will run best on?-- WcW, Jan 12 2009 Why not indeed? [+]-- MaxwellBuchanan, Jan 12 2009 I think the computer makes some assumptions about how it would expect fuel to behave, and then trims here and there based on its arsenal of sensors. If it detects a problem, e.g. detonation, it reacts accordingly with a step change into 'safe' mode.
I don't think the computer is actively looking for the performance limits of the fuel. It just assumes the limits, which 99% of the time are valid assumptions (with a bit of head room).-- Texticle, Jan 12 2009 A problem is that, as far as I know, fuels and octane ratings are made by burning them in an engine and comparing it to iso-octane. There's no easy chemical test for fuel quality, especially with whatever additives are in it.
I suppose there could be a function that lets the engine run idle for a few moments, and calculates a rough idea of fuel quality from that, comparing it to an ideal fuel that they run in the car when it's produced.
But it wouldn't really be worth it, since a higher octane fuel would make no improvement in performance to an engine with a compression ratio designed for a lower octane number. The best thing would be to have the fuel the engine was designed for written on the dashboard, and you'd always know that's the best fuel to use, it's not going to change.-- mitxela, Jan 12 2009 nowadays the EMS is constantly adjusting the ignition timing and A/F ratio to maximize fuel economy. This means it has good data on the tendency to knock and the specific fuel density (fuel volume required to achieve a clean burn) thus as good a measure of the fuel quality as you will ever have. In addition the computer has access to data about overall fuel economy and can interpolate that into the mix. Specifically I was thinking of sportier cars where high compression or turbocharging make fuel quality crucial. In these cars the computer is already making this kind of evaluation and could be sending the information to the OBC so we can see it.-- WcW, Jan 13 2009 random, halfbakery