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  #16  
Old 01-28-2018, 01:05 PM
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A big reason this technology wasn't viable before was that computers weren't fast enough. In order to get the fuel detonating at the exact right time, the computer has to control each cylinder closed loop and make microsecond decisions based on speed, load, changing throttle input, etc. We're finally seeing embedded systems that can run such tasks.

Same goes for common rail diesels that monitor the cylinder pressure of each cylinder and precisely control fuel timing for the most efficient burn. I had a job towing/hauling with ford 6.7 diesels, amazingly smooth engines. They'll start up in the dead of winter with 3 seconds of glow without being plugged in, it's insane.
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  #17  
Old 01-28-2018, 07:05 PM
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And even though many modern diesels are direct injection, they are super quiet. ( unless some idiot installs a tuner box ) The injectors don't give a single sudden burst of fuel like a mechanical pump, the give a few slight puffs to get combustion going then give the main charge.

Another bit of info on modern computer diesels. In tow / haul mode, they offer engine braking. Some of this is from the back pressure flap in the exhaust used for faster warm up serving double duty as an engine brake. The other bit is from altering fuel timing by advancing it far enough that the flame occurs as the piston is rising making the engine work against it's self.

Some will make a big fuss how their low power, leaky, stinky , inefficient mechanical diesel is the only way a diesel should be made. With modern controls there isn't much reason to live with these ills. People buy a _new_ vehicle for what it does right now not what it might do in 30 years.
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  #18  
Old 01-28-2018, 07:25 PM
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Yea, I agree. It's tiring seeing things like "the only real diesel is mechanic, blah blah".
I like to live in a world between... I like the old classics, who doesn't! But it's hard not to be enamored with a diesel of the same displacement that makes three times the power, doubles economy, and sounds like a honda.
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  #19  
Old 01-30-2018, 10:47 AM
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As post 13, I was also thinking they must form a "stratified charge", i.e. a region closer to stoichiometric where the spark can ignite. A mixture of gasoline vapor and air has a narrow O/F region where it will ignite. For best efficiency at low power, one would like to run much leaner than that. By stratifying the O/F distribution, the average mixture for the whole cylinder can be leaner, but still ignite. Diesel ignition is the different phenomenon of "droplet combustion", where a flame burns around each droplet in a close-to-stoichiometric region.

The main reason for improved efficiency, per thermodynamics theory, is a higher compression ratio, and less throttling, both of which make diesels more efficient than typical gas engines. While such ideas have been around for a century, technology now allows some to be realized. Note they mention the engine controller adjusting, based on pressure rise rate. This suggests a piezo-electric sensor monitoring cylinder pressure. These have long been around, but are cheaper and common now in knock sensors. Also, catalytic converters have greatly improved and are now "3-way" type which reduce NOx directly (rather than old, klutsy EGR method of reducing exhaust temperature). I recall reading that changed NOx rules killed the 1980's stratified-charge designs.

Re "why improve gas engines when vehicles are going electric?", think of supply and demand. As more become electric, gasoline prices will drop. Best thing for us greasers would be many Tesla electric semis, though I see them as mainly marketing hype. More electrics may push up the price of battery commodities (lithium today, other metals next month). So, I expect hydrocarbon vehicles to last thru the century, just as gas and diesel vehicles have co-existed.
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  #20  
Old 01-30-2018, 01:59 PM
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Quote:
Originally Posted by Diseasel300 View Post
I have to wonder if these new engines are going to be using massive amounts of EGR with a cooler like the modern diesel truck engines do to meet emissions standards...
Yes, you're correct. It says that the article.
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  #21  
Old 01-30-2018, 05:45 PM
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Quote:
Originally Posted by BillGrissom View Post
Note they mention the engine controller adjusting, based on pressure rise rate. This suggests a piezo-electric sensor monitoring cylinder pressure. These have long been around, but are cheaper and common now in knock sensors.

SAAB did knock sensing with the spark plug starting in 1993 by monitoring secondary current and wave form. This system was called " Trionic" . When detonation occurs, cylinder pressures rise making it more difficult to keep an arc going.
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