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K13 Tuning & Mechanical
Techtalk/Guide: HR12DDR - DIG-S
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<blockquote data-quote="G-Zee" data-source="post: 592228" data-attributes="member: 15831"><p>For what its worth the dig-s engine is not a true miller cycle engine. The original miller cycle engine design from 70 years ago used an unusual double cranking mechanism to allow the piston to take a shorter compression stroke than expansion stroke. Unfortunately the crank arrangement introduced more inefficiency than was gained from the long expansion stroke. Some time in the 90s Mazda introduced a 3 litre V6 with what they called esoteric valve timing to achieve the miller cycle. Press referred to engine as 5 stroke. The engine was only available as an expensive optional extra on the not so popular Zedos 9. Think they may have called it Millertime? Mazda also quoted the engine as 2.3 l not 3 l measuring the compression stroke only with valves closed. Without variable valve timing the engine needed forced induction at all revs only achievable with a lysholm compressor (think dig-s supercharger is lysholm type) This engine was very good but not a sales success. Move forwards to today and latest prius and yaris hybrid engines are 1.8 and 1.5 engines which run a valve timing based miller cycle. No supercharger is needed as the electric motor attached to the engine replaces the need preventing the engine stalling at low revs. Also we have the dig-s engine and the Fiat twin-air engines which can run miller cycle. In case of the Fiat the engine which has non mechanically actuated inlet valves operates in 5 different modes involving lean burn, miller and stoichiometric - I.e. conventional perfect air fuel ratio. Unfortunately where the Fiat engine on paper is an absolute work of genius - in reality its just not that good needin revved hard to get any power which is never that much and returning about 35mpg. I'm not sure whether the dig-s works like the Mazda constant miller cycle or the Fiat. I believe Nissan system is like the Fiats using constantly variable timing to operate in different modes which should be better. The dig-s is certainly a very refined engine with good mid range power but fuel economy has been a bit of a disappointment.</p><p></p><p>Sent from BlackBerry 9790 using Tapatalk</p></blockquote><p></p>
[QUOTE="G-Zee, post: 592228, member: 15831"] For what its worth the dig-s engine is not a true miller cycle engine. The original miller cycle engine design from 70 years ago used an unusual double cranking mechanism to allow the piston to take a shorter compression stroke than expansion stroke. Unfortunately the crank arrangement introduced more inefficiency than was gained from the long expansion stroke. Some time in the 90s Mazda introduced a 3 litre V6 with what they called esoteric valve timing to achieve the miller cycle. Press referred to engine as 5 stroke. The engine was only available as an expensive optional extra on the not so popular Zedos 9. Think they may have called it Millertime? Mazda also quoted the engine as 2.3 l not 3 l measuring the compression stroke only with valves closed. Without variable valve timing the engine needed forced induction at all revs only achievable with a lysholm compressor (think dig-s supercharger is lysholm type) This engine was very good but not a sales success. Move forwards to today and latest prius and yaris hybrid engines are 1.8 and 1.5 engines which run a valve timing based miller cycle. No supercharger is needed as the electric motor attached to the engine replaces the need preventing the engine stalling at low revs. Also we have the dig-s engine and the Fiat twin-air engines which can run miller cycle. In case of the Fiat the engine which has non mechanically actuated inlet valves operates in 5 different modes involving lean burn, miller and stoichiometric - I.e. conventional perfect air fuel ratio. Unfortunately where the Fiat engine on paper is an absolute work of genius - in reality its just not that good needin revved hard to get any power which is never that much and returning about 35mpg. I'm not sure whether the dig-s works like the Mazda constant miller cycle or the Fiat. I believe Nissan system is like the Fiats using constantly variable timing to operate in different modes which should be better. The dig-s is certainly a very refined engine with good mid range power but fuel economy has been a bit of a disappointment. Sent from BlackBerry 9790 using Tapatalk [/QUOTE]
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