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Old 01-29-2012, 02:38 PM
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please help.

hi yall i need your help very badly. so im writing this paper for school on gas vs diesel engines and how much they pollute. Would you guys give me any facts that you may know about this subject. I dont care what diesel motor or whatever but just some fluff to make the diesel not sound so bad
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Old 01-29-2012, 03:24 PM
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Well new diesel engines with all the emissions stuff will pollute less. The exhaust is cleaner with the dpf and def its almost cleaner going out then it is. plus diesel is more efficient than gas so it has more usable energy compared to gas. Then if you really want something to write there is biodiesel that is really clean. And in europe 60% of vehicles are diesel so that says a lot there Europe is crazy about emissions stuff.
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Old 01-29-2012, 03:39 PM
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there was an article is diesel power a couple years ago about this very thing. I wish I had my old magazines but i threw them out recently. Diesel's also emit less co2 (cardon dioxide) than gas, but more NOx (nitrous oxides) and SOx (sulfor oxides)
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Old 01-29-2012, 04:02 PM
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The diesel smoke that you see is not gaseous, it is particulate.

Do some quick research on cats. Gasoline engines have dual bed converters that work on the concept of reduction and oxydation. The front bed reduces and the rear bed oxydizes.

I believe that diesel converters reduce only but I am not 100% on that. You will also need to find info on the new cats that go through regen and how much greater the diesel emissions are when they are in regen mode.

Keep in mind the simple science behind engines. What goes in must come out. Take your air: oxygen, nitrogen, carbon dioxide, etc, etc and your fuel: carbon and hydrogen. All of these combine to become your exhaust.

You need to research the BTUs in gasoline vs. diesel fuel to see if you can put together an idea of which is more powerful and then tie together the work of 1 gallon of gas vs 1 gallon of diesel, the emissions of each and then the emissions for the amount of work done. For a twist you can then offset the diesel emissions if it is soy based biodiesel with the carbon dioxide consumed/oxygen generated by the soy bean plants growing in the field to make the fuel.

Then the question comes up of how does the particulate diesel emissions and the gaseous emissions from a diesel compare to that of gaseous only from gasoline.

Hope some of these point you in the right direction.
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Old 01-29-2012, 04:23 PM
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Thanks everybody for the information
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Old 01-29-2012, 04:30 PM
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another thing is that any diesel engine is going to pollute les than any gas engine of the same size, example would be 7.3 powerstroke compared to 460 v8
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Old 01-29-2012, 08:45 PM
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i actually learned a lil from this myself, wish i had something smart to contribute. i hope you do good on your paper and your teacher doesent drive a prius! hahaha
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Old 01-29-2012, 09:40 PM
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Quote:
Originally Posted by Red '97 View Post
another thing is that any diesel engine is going to pollute les than any gas engine of the same size, example would be 7.3 powerstroke compared to 460 v8
This is a bit of a flawed generalization. Too many factors contribute to pollution. Air to fuel ratio, compression ratio, naturally aspirated vs forced induction, to name a few.

Anyways,
Properly tuned diesel engines generally run slightly below a stoichiometric ratio, meaning there is more oxygen than required to completely burn fuel. This means CO and CO2 emissions are lower with a diesel engine. Flip side of this is that diesel combusts at a much higher temperature than gas, which leads to higher NOx emissions. Modern catalytic convertors do a pretty good job of eliminating NOx, so this is becoming less and less of an issue. Also, even low sulfur diesel contains sulfur, which means SO2 (sulfur dioxides) are higher with diesel.
Bring up the lack of a throttle butterfly which causes diesels to be much more efficient than a gas engine at low rpm. Typical gas engines operate at less than 35% efficiency at idle. Power in a gasoline engine is limited by the throttle plate, meaning airflow is restricted. A diesel limits power by limiting fuel, but maintains airflow regardless.
Diesel contains 128,700 BTU/Gal compared to 115,500 BTU/Gal for gasoline, meaning it is more energy dense than gas. A gallon of diesel is capable of more ‘work’ (force x distance) than gas.
Diesel is also rated in terms of cetane as opposed to octane for gas. The cetane number of a fuel is a measure of it’s ignition delay; basically the time period between the start of injection and the first identifiable pressure increase (combustion). Higher cetane number will have a shorter ignition delay, and vice-versa. Gasoline on the other hand is rated in terms of octane, which evaluates its ability to resist pre-ignition (or compression ignition).
This allows diesel engines to accomplish two things. 1) Run higher compression ratios than gasoline because they are not ‘knock limited’ (18:1 as opposed to a maximum of roughly 10:1) 2) Makes forced induction much easier, which increases efficiency throughout the powerband. Basically a gas engine can be tuned to provide optimal fuel-air ration at low rpm or high rpm, whereas a properly tuned forced induction, high compression diesel maintains the stoichiometric ratio throughout the entire operating range.

Hope all of this makes sense…I’m known to ramble after a long day.
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Old 01-30-2012, 09:23 AM
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thats a whole lot of information in one post haha, awesome info thanks man!
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Old 01-31-2012, 04:45 PM
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Quote:
Originally Posted by backwoodsboy View Post
This is a bit of a flawed generalization. Too many factors contribute to pollution. Air to fuel ratio, compression ratio, naturally aspirated vs forced induction, to name a few.

Anyways,
Properly tuned diesel engines generally run slightly below a stoichiometric ratio, meaning there is more oxygen than required to completely burn fuel. This means CO and CO2 emissions are lower with a diesel engine. Flip side of this is that diesel combusts at a much higher temperature than gas, which leads to higher NOx emissions. Modern catalytic convertors do a pretty good job of eliminating NOx, so this is becoming less and less of an issue. Also, even low sulfur diesel contains sulfur, which means SO2 (sulfur dioxides) are higher with diesel.
Bring up the lack of a throttle butterfly which causes diesels to be much more efficient than a gas engine at low rpm. Typical gas engines operate at less than 35% efficiency at idle. Power in a gasoline engine is limited by the throttle plate, meaning airflow is restricted. A diesel limits power by limiting fuel, but maintains airflow regardless.
Diesel contains 128,700 BTU/Gal compared to 115,500 BTU/Gal for gasoline, meaning it is more energy dense than gas. A gallon of diesel is capable of more ‘work’ (force x distance) than gas.
Diesel is also rated in terms of cetane as opposed to octane for gas. The cetane number of a fuel is a measure of it’s ignition delay; basically the time period between the start of injection and the first identifiable pressure increase (combustion). Higher cetane number will have a shorter ignition delay, and vice-versa. Gasoline on the other hand is rated in terms of octane, which evaluates its ability to resist pre-ignition (or compression ignition).
This allows diesel engines to accomplish two things. 1) Run higher compression ratios than gasoline because they are not ‘knock limited’ (18:1 as opposed to a maximum of roughly 10:1) 2) Makes forced induction much easier, which increases efficiency throughout the powerband. Basically a gas engine can be tuned to provide optimal fuel-air ration at low rpm or high rpm, whereas a properly tuned forced induction, high compression diesel maintains the stoichiometric ratio throughout the entire operating range.

Hope all of this makes sense…I’m known to ramble after a long day.
Add to this good info that EGR is used to reduce NOx. The exhaust gas that is routed to the intake manifold is an inert filler that cools the combustion temp.

Sent from my DROID X2 using Tapatalk
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