Someone should try driving a course by accelerating in 5th gear, and then costing a bit in neutral, then accelerate again. The engine would spend more time at full throttle, where thermal efficiency is higher.
Possible future engine efficiency enhancements
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I think you are all missing something.
Take for example a car I used to own: a 1964 Chevy Biscayne, with a 240 cid inline 6 and a "3 on the tree" manual transmission. I have no idea what the RPMs were, but that car would do just over the ton and in 65-70 mph driving (interstate) get about 23 mpg. 18 mpg around town.
versus
2002 Honda Accord V6 Sedan. 200HP, 200tq. low 20's around town, up to 30 on the highway.
The difference? Emissions. As you go more and more lean burn, NOx and friends go up dramatically. That V6 /could/ do vastly better but the EPA won't let it. The Chevy won't ever do much better, but it won't come even close to meeting any emissions just about anywhere.
A third example. 2000 Chevy Suburban 2500 HD, 6.0L engine. 18 mpg around town, 24 on the road. How is this accomplished? It doesn't even have cyl. deactivation! Tall gear ratios and lots of torque, with an efficient and clean burn. True, the Honda meets LEV (or ULEV) and the Suburban doesn't. See? If the suburban had to meet the *same* emissions, *something* would have to give, and all other things being equal, mileage is one of them.
Mileage != emissions. Emissions is NOT JUST particulates. Emissions *these days* means a whole soup of crap the EPA mandates.
Don't get me started on oxygenated fuel. I hate oxygenated fuel, but I hate MTBE more than ethanol. I hate them both, however. That's a different issue.
Take for example a car I used to own: a 1964 Chevy Biscayne, with a 240 cid inline 6 and a "3 on the tree" manual transmission. I have no idea what the RPMs were, but that car would do just over the ton and in 65-70 mph driving (interstate) get about 23 mpg. 18 mpg around town.
versus
2002 Honda Accord V6 Sedan. 200HP, 200tq. low 20's around town, up to 30 on the highway.
The difference? Emissions. As you go more and more lean burn, NOx and friends go up dramatically. That V6 /could/ do vastly better but the EPA won't let it. The Chevy won't ever do much better, but it won't come even close to meeting any emissions just about anywhere.
A third example. 2000 Chevy Suburban 2500 HD, 6.0L engine. 18 mpg around town, 24 on the road. How is this accomplished? It doesn't even have cyl. deactivation! Tall gear ratios and lots of torque, with an efficient and clean burn. True, the Honda meets LEV (or ULEV) and the Suburban doesn't. See? If the suburban had to meet the *same* emissions, *something* would have to give, and all other things being equal, mileage is one of them.
Mileage != emissions. Emissions is NOT JUST particulates. Emissions *these days* means a whole soup of crap the EPA mandates.
Don't get me started on oxygenated fuel. I hate oxygenated fuel, but I hate MTBE more than ethanol. I hate them both, however. That's a different issue.
BMW uses the valves to act as throttles to limit airflow, while diesels are still unthrottled. So you still have a fundamental difference in operation (limiting airflow vs. limiting fuel flow).
Diesel fuel still has more energy per given mass because it is more dense than gasoline (even though we buy fuel based on volume), so with gas you are already at a disadvantage.
This is a great thread.
If you ever raced cars on the track you would be used to looking way ahead in traffic. My normal driving is to step on it hard to get going. But then I look 1/4 mile ahead to see if I should speed up or coast the 'rest of the way. I rarely use my brakes.
People are getting 15 - 30 k on Mercedes brakes in town. I get 60 - 70 k. All I do for the most part is city traffic.
In all my cars I get the highway rated miles / gallon. I do believe it is because I run in the more efficient area of the engine curve.
aehaas
Does anyone here drive a turbodiesel car?
I just realized that the intercooler robs thermal energy from the engine, and should be disabled when you don't need lots of power.
The intercoler allows more air to be pumped into the engine, so you can get more power, but when cruising down the highway, you don't need it, and in fact it just wastes heat energy to the outside air.
Someone who drives a turbodiesel powered car might want to try, on their next road trip, putting a sheet of cardboard over the intercooler air inlet to block the airflow. This will reduce the maximum power you get out of the engine, but it should improve fuel economy a bit.
The best arrangement would be to switch the intercooling on and off depending on need.
I just realized that the intercooler robs thermal energy from the engine, and should be disabled when you don't need lots of power.
The intercoler allows more air to be pumped into the engine, so you can get more power, but when cruising down the highway, you don't need it, and in fact it just wastes heat energy to the outside air.
Someone who drives a turbodiesel powered car might want to try, on their next road trip, putting a sheet of cardboard over the intercooler air inlet to block the airflow. This will reduce the maximum power you get out of the engine, but it should improve fuel economy a bit.
The best arrangement would be to switch the intercooling on and off depending on need.
Put a rotary heat exchanger on a diesel engine. When you need cold air for maximum power, stop rotating the heat exchanger element. This should give a few more % efficiency.
Raising your intake charge-temp will also give you an increase in exhaust-gast temps (EGT).
May not be an issue, but it could be especially if you have modified your engine to make more power (thus more EGT), or if you suddenly decide that you need power after all (say, you encounter a steep hill on your drive, which will also increase EGT).
May not be an issue, but it could be especially if you have modified your engine to make more power (thus more EGT), or if you suddenly decide that you need power after all (say, you encounter a steep hill on your drive, which will also increase EGT).
When you need power, the heat recovery can be switched off. When cruising down the highway at low power, the increased temperatures will result in higher cylinder pressures, and higher thermal efficiency.
Some diesel cars, though, like the VW's, have engines that already get their best thermal efficiency when putting out about 30 hp, which is about what you need to go 75 mph. This modification would work better for the diesel pickups, when they're not towing stuff and working at very low power levels.
Some diesel cars, though, like the VW's, have engines that already get their best thermal efficiency when putting out about 30 hp, which is about what you need to go 75 mph. This modification would work better for the diesel pickups, when they're not towing stuff and working at very low power levels.
They beat me to it:
http://www.energy.gov/engine/conten...BT_CODE=PR_PRESSRELEASES&TT_CODE=PRESSRELEASE
near the bottom:
"Caterpillar Inc. in Peoria, IL will develop a new air management and exhaust energy recovery system for commercial diesel engines. Electric turbocompounding and high efficiency air system technology will be key technology building blocks developed. Additional system elements may be developed to support the energy recovery system. Advanced engine system concepts that further enable exhaust energy recovery may also be investigated.
DOE cost: $3,934,862. Industry cost share: $3,934,862 "
http://www.energy.gov/engine/conten...BT_CODE=PR_PRESSRELEASES&TT_CODE=PRESSRELEASE
near the bottom:
"Caterpillar Inc. in Peoria, IL will develop a new air management and exhaust energy recovery system for commercial diesel engines. Electric turbocompounding and high efficiency air system technology will be key technology building blocks developed. Additional system elements may be developed to support the energy recovery system. Advanced engine system concepts that further enable exhaust energy recovery may also be investigated.
DOE cost: $3,934,862. Industry cost share: $3,934,862 "
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