Re: Why Can't A Fuel injected Petrol Engine be as Efficient as a Diesel?

Do we have more efficient when we put compress air in gasoline engine? Why does turbo engine never work well in most car?


<bernxard@xxxxxxxxxxxx> wrote in message news:1116600309.774052.51540@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> A gasoline engine always burns its fuel 'stoichiometrically' that is 14
> parts by weight air to 1 part by weight gasoline so that there is a
> complete burn of both oxygen and fuel.
>
> When running at partial power this leads to suction losses as the
> airflow is throttled. If you halve the fuel flow you also have to
> halve the airflow. (strictly speaking it is airflow that determines
> fuel flow)
>
> The diesel opperares with an over supply of air, it never throttles the
> airflow and only controls power by controlling fuel flow. It's as if
> the piston bounces of air at the top of the stroke as a spring would
> and all of the energy is returned.
>
> when running at near 100% of power there is little differences in fuel
> efficiency: the gains are mainly in the area of partial load.
>
> There is a type of petrol engine called a 'lean burn engine' which
> tries to opperate on partially lean mixtures. Getting good ignition
> tends to require fancy injection systems to try and get a 'stratefied
> charge' ie a rich mixture near the sparking plug. Can be done with
> direct injection AFTER the compression stroke is complete rather than
> multipoint injection during the induction stroke.
>
> Iridium based catalysts that destroy nirtrous oxides also appear part
> of the solution to stratefied charge engines and this requires low
> sulfur fuels.
>
> High compression does lead to improvements in efficiency but only up to
> a point (about 13:1) because more of the energy can be expanded. Part
> of the reason is for diesels high compression is to get good ignition.
>
.

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