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Originally Posted by Arragonis
Which diesels have a throttle plate ? Just interested.
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The VW 2.0 TDI has one to assist with EGR flow and assist with light load stoichiometric operation for the purpose of regenerating the NOx catalyst. I do not know what position the throttle plate goes to on deceleration.[/QUOTE]
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Diesels have more engine braking, higher gearing may mask it somewhat. A diesel in 4th may brake as much as a petrol in 4th but the rpms would be very different with the petrol being higher. Higher rpms = more compression strokes, Diesels have more compression for each stroke.
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Again, remember that on deceleration, compression is a giant spring. While higher compression may be harder to push against on the compression stroke, it forces the piston down much harder on the power stroke, thereby turning the engine and cancelling out any energy lost during the compression stroke (inefficiencies aside), so no more power is needed to rotate an engine with a higher compression ratio vs one with a lower compression ratio.
A compression brake (on larger diesels), aka "Jake Brake", solves this by opening the exhaust valve just before TDC on the compression stroke to exhaust the compression pressure to keep the giant compression spring from forcing the piston back down.