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Re: Diesel opacity tests for road vehicles
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Posted by KEB on September 23, 2006 at 14:39:18 from (207.94.27.8):
In Reply to: Re: Diesel opacity tests for road vehicles posted by Bob on September 23, 2006 at 11:25:56:
"The pump adjustment controls the MAX amount of fuel injected with the pedal to the floor..." TRUE, sort of "...have NO EFFECT on the fuel rate at less than WOT" NOT TRUE. In a rotary injection pump, the length of the plunger stroke is constant regardless of the throttle setting, not controlled by the throttle setting like the old in-line pumps. The amount of fuel delivered in each stroke of the plunger is controlled by opening the metering valve some number of rotational degrees after the start of the plunger stroke, spilling excess fuel back into the pump housing. The point at which the metering valve opens is determined by a combination of engine speed and throttle setting. Essentially, fuel is delivered for some percentage of the plunger stroke. What you're actually adjusting when you turn the pump up or down is the maximum stroke of the plunger, which does control the maximum amount of fuel the pump can deliver at wide open throttle, PROVIDED ENGINE SPEED IS BELOW GOVERNED SPEED. At top speed, the governor mechanism in the pump will start opening the metering valve earlier, reducing the total amount of fuel. Since the opening point of the metering valve is at some percentage of the plunger stroke, as determined by the position of the throttle and engine speed (via the governor), a longer maximum stroke will result in greater fuel delivery at a fixed throttle position and speed. Conversely, a shorter maximum stroke, i.e., turning down the pump, will deliver less fuel at a particular throttle setting and speed. Since a diesel has not throttle plate, air volume is a function of speed, and reducing the fuel at a give speed leans the burn, reducing smoke. Same reason they smoke at higher altitudes if set for a low altitude...thinner air results in fewer air molecules in the combustion chamber and a richer burn. There's a relatively simple desription of a rotory injection pump operation at the attached link. The mechanical arrangement of the Bosch pump is different than the Roosa-Master, but the prinicple of operation is the same. I couldn't find a simple description of the Roosa-Master pump & wasn't going to spend a lot of time looking for one. Hope this helps. Keith
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