[Diy_efi] Intro, and q's about fuel economy

[Greg Hermann]

At 10:49 AM 12/16/02, Alexei Pavlov wrote:
>pedward at apsoft.com wrote:
>>
>> > What the EGR really does is reduce the pumping losses at cruise due to
>> > throttling.
>>
>> It's simpler than that.  The exhaust gases already have fuel in them to
>> some degree.  You recycle that in place of actual fuel.  The only way to
>>eliminate
>> throttle losses is to have no throttle at all.  You then do the
>>throttling via
>> modulation of the valve timing.
>
>Could you explain why there are no pumping losses with variable valve
>timing or clearance ?
>I see variable valves exactly like throttles, the piston still has to
>pump the vacuum to reach the BDC. The energy loss is still here.
>
Correct with respect to variable valve lift/timing .

The way that EGR reduces pumping losses is by providing an inert diluent
for the fuel/sir mixture, thus avoiding any need for a throttle. It DOES
hurt cycle efficiency, however--because it usually lowers the peak cycle
temperature (unless, of course, you use really HOT exhaust for the EGR !

Greg



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