I've always wondered about that...
and can somebody explain the difference between compression ignition and spark ignition?
Thanks...
and can somebody explain the difference between compression ignition and spark ignition?
Thanks...
why are diesels louder? ..
- Thread starter 97tbird
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The compression ratio of most daily-driven gas engined vehicles is anywhere from about 8.5 - 11.0 to one. Diesels, OTOH, typically have CRs anywhere from about 22.0 - 26.0 to one. The higher compression is used with a glow plug (think heating element) to basically super-squeeze the diesel fuel so much, that the glow plugs heat ignites the compressed diesel/air mixture. Any diesel experts out there feel free to add/correct this info.
The glow plugs are only used for start up during cold weather, otherwise the compression does the ignition.....
TomH,
thanks alot for the explnantion...does this "glow plug" have an electrical supply?
And why are diesel engines louder?
Thanks again..
Glow plugs are used to aid in starting a diesel engine. They are only on for a brief period of time before starting the engine. Not all diesel engines have glow plugs, commercial diesel trucks mainly do not have them.It was mainly older, poorly designed diesels that had to have them (olds, gm, vw rabbit). Diesel engines sound different because they fire by compression ignition.
On a typical 4 stroke gas engine, you have 4 strokes that do different functions 1 intake, 2 compression (the spark plug fires the gas/air here on most engines just before top dead center (i.e. example, timing set at 8 degees btdc), 3 power. The only thing different on how the diesel fires is that the very high compression ratio self ignites the fuel instead of a spark plug doing it. And yes, glow plugs have electric current to them when needed.
From free auto advice web site:
Diesel engines have been around for a long time. They are the powersource of choice for heavy trucks, boats, generators and equipment. They are a lot more popular in cars in the rest of the world than in the U.S. Probably due to gasoline prices and lower emmisions standards. Diesel engines have become a lot more high tech in the past ten years. Most manufacturers are switching over to electronic fuel management. Diesel engines differ from gas engines in a couple of ways.
1.
Diesel fuel is less refined than gas. This means that diesel will explode if compressed enough. It does not require a spark.
2.
Diesels must be fuel injected. They only suck in as much air as they need. unlike gas engines which will rev higher and higher if unrestricted.
3.
To get more power from a diesel usually requires a turbo to push in more air.
4.
Diesels require higher compression than gas engines due to the fuel quality.
5.
Diesels engines are generally noisy due to this high detonation pressure.
6.
Diesels are built a lot tougher due to this detonation also. Stronger internal parts, larger oil and coolant capacities,etc.
7.
Getting 250,000 miles from a diesel without any repairs is normal.
8.
Diesels cannot rev as high as a gas engine due to higher reciprocating mass.
9.
Diesel engines make a truck sound tough.
10.
Click Here to Hear a Diesel Running!(Ford 7.3 Indirect Injected)
11.
On newer engines for heavy trucks, such as Caterpillar's 3406E, You can buy a truck with a 325 horsepower engine. Down the road you decide it doesn't have enough power. For about $1500 you go to the dealer, he hooks up a laptop, tells the same engine that you've been driving all this time (the 325 horse engine) to go ahead and make 400 horsepower.You leave with 400 horses, nothing mechanical done to the engine. Just software. Cool huh? Is this the wave of the future for sports cars?
Diesel engines have been around for a long time. They are the powersource of choice for heavy trucks, boats, generators and equipment. They are a lot more popular in cars in the rest of the world than in the U.S. Probably due to gasoline prices and lower emmisions standards. Diesel engines have become a lot more high tech in the past ten years. Most manufacturers are switching over to electronic fuel management. Diesel engines differ from gas engines in a couple of ways.
1.
Diesel fuel is less refined than gas. This means that diesel will explode if compressed enough. It does not require a spark.
2.
Diesels must be fuel injected. They only suck in as much air as they need. unlike gas engines which will rev higher and higher if unrestricted.
3.
To get more power from a diesel usually requires a turbo to push in more air.
4.
Diesels require higher compression than gas engines due to the fuel quality.
5.
Diesels engines are generally noisy due to this high detonation pressure.
6.
Diesels are built a lot tougher due to this detonation also. Stronger internal parts, larger oil and coolant capacities,etc.
7.
Getting 250,000 miles from a diesel without any repairs is normal.
8.
Diesels cannot rev as high as a gas engine due to higher reciprocating mass.
9.
Diesel engines make a truck sound tough.
10.
Click Here to Hear a Diesel Running!(Ford 7.3 Indirect Injected)
11.
On newer engines for heavy trucks, such as Caterpillar's 3406E, You can buy a truck with a 325 horsepower engine. Down the road you decide it doesn't have enough power. For about $1500 you go to the dealer, he hooks up a laptop, tells the same engine that you've been driving all this time (the 325 horse engine) to go ahead and make 400 horsepower.You leave with 400 horses, nothing mechanical done to the engine. Just software. Cool huh? Is this the wave of the future for sports cars?
Diesels are louder because of the compression ratio, and because they're compression ignition. So the cylinder pressures are higher, since the "bang" is releasing more energy. I also wanted to clarify that a diesel's ignition timing is controlled soley by the fuel injector timing. The compression heats the air up enough for a burn, then once the fuel gets squirted in, you have ignition.
Manufacturers are spending a lot of R&D money trying to quiet diesels down, and the results have been pretty favorable. Injector timing and pressure play a large role. There are also systems that do multiple injections, like a couple small ones before the big shot, and this has helped, also. I think reducing NVH is going to play a key role in how warmly the US embraces passenger car diesels. The power (and torque) and economy is already here.
Manufacturers are spending a lot of R&D money trying to quiet diesels down, and the results have been pretty favorable. Injector timing and pressure play a large role. There are also systems that do multiple injections, like a couple small ones before the big shot, and this has helped, also. I think reducing NVH is going to play a key role in how warmly the US embraces passenger car diesels. The power (and torque) and economy is already here.
Tbird, another reason diesels are loud in this country is that just about the only ones you see are commercial truck engines. The pickups that use diesels use good solid commercial truck engines that weren't designed with quiet as a high priority.
Modern passenger car diesels are quiet enough that your wife probably wouldn't notice them. They had to work hard to get them that quiet.
Modern passenger car diesels are quiet enough that your wife probably wouldn't notice them. They had to work hard to get them that quiet.
An additional reason is, diesels like as little backpressure as possible. You essentially can't go too big on the exhaust. So you are more likely to be offended by a diesel since the exhaust system has been altered by the owner to be as unrestrictive as possible. Kinda like Harleys...except they're not diesels, just really, really obnoxious.
from my bosch auto handbook:
you can state this to the wife in a monotone voice
the combustion process, which begins with the start of ignition, can be subdivided into two phases. In the "premixed flame" phase, the fuel injected prior to the start of ignition and mixed with air combusts. The fuel which is injected after the start of ignition combusts in a "diffusion flame". The portion of the combusted fuel which burns as a very rapid premixed flame is primarily responsible for the pressure increase, and thus the primary cause of combustion noise....
Due to the abrupt combustion of the vaporized fuel mixed with air, the autoignition process is characterized by "hard combustion" which is often very loud.
--------------
FYI:
spark ignition is exactly that, fuel mixture ignited by a spark (i.e. spark plug). In Compression ignition the fuel is ignited by the heat generated by compression of the volume of gas (i.e. air) in the cylinder. Gasoline engines have compression ratios ranging from 8:1 to 10.5:1 on average and can run as high as 12:1. The important thing to know is that it's cylinder pressure and not really compression ratio (because of intake and exhaust valve overlap) that determines the point of fuel pre-ignition or compression ignition. In gasoline engines, for typical 93 octane, cylinder pressures can't exceed 200psi without running into preignition. On diesels, compression ratios are at least 17:1, depending on year and model, and have cylinder pressures of ranging from 400-800psi, depending on engine design. The compression test I did on my 1989 7.3L ford ran in the 550psi range. When any gas in compressed, it is heated. The piston simply compressing air to 400-800psi causes it's temperature to increase to 700-900C (1300-1650F) which is sufficient to ignite the fuel. It is important to note, that the fuel is not mixed with air prior to entering the cylinder, like on a gas engine. Diesel is injected (via fuel injector) into the cylinder when the piston is near top dead center and cylinder pressure is 800psi and 900 deg. C. As soon as the fuel is injected, it ignites, producing work. Injector line pressures on the diesels of today run around 3000psi I believe- on the bosch common rail injection. On my 1989 7.3L, injector pop open pressure spec is 1400psi minimum; new injectors 1700psi.
[ October 21, 2004, 01:33 PM: Message edited by: 1 FMF ]
you can state this to the wife in a monotone voice
the combustion process, which begins with the start of ignition, can be subdivided into two phases. In the "premixed flame" phase, the fuel injected prior to the start of ignition and mixed with air combusts. The fuel which is injected after the start of ignition combusts in a "diffusion flame". The portion of the combusted fuel which burns as a very rapid premixed flame is primarily responsible for the pressure increase, and thus the primary cause of combustion noise....
Due to the abrupt combustion of the vaporized fuel mixed with air, the autoignition process is characterized by "hard combustion" which is often very loud.
--------------
FYI:
spark ignition is exactly that, fuel mixture ignited by a spark (i.e. spark plug). In Compression ignition the fuel is ignited by the heat generated by compression of the volume of gas (i.e. air) in the cylinder. Gasoline engines have compression ratios ranging from 8:1 to 10.5:1 on average and can run as high as 12:1. The important thing to know is that it's cylinder pressure and not really compression ratio (because of intake and exhaust valve overlap) that determines the point of fuel pre-ignition or compression ignition. In gasoline engines, for typical 93 octane, cylinder pressures can't exceed 200psi without running into preignition. On diesels, compression ratios are at least 17:1, depending on year and model, and have cylinder pressures of ranging from 400-800psi, depending on engine design. The compression test I did on my 1989 7.3L ford ran in the 550psi range. When any gas in compressed, it is heated. The piston simply compressing air to 400-800psi causes it's temperature to increase to 700-900C (1300-1650F) which is sufficient to ignite the fuel. It is important to note, that the fuel is not mixed with air prior to entering the cylinder, like on a gas engine. Diesel is injected (via fuel injector) into the cylinder when the piston is near top dead center and cylinder pressure is 800psi and 900 deg. C. As soon as the fuel is injected, it ignites, producing work. Injector line pressures on the diesels of today run around 3000psi I believe- on the bosch common rail injection. On my 1989 7.3L, injector pop open pressure spec is 1400psi minimum; new injectors 1700psi.
[ October 21, 2004, 01:33 PM: Message edited by: 1 FMF ]
here is a link that explains diesel engines pretty well.
How Diesel Engines Work
How Diesel Engines Work
Harleys aren't diesel???
Thanks a lot,guys...
I finally understood some things about diesels now.
My wifey, hearing how noisy the neighbor's diesel truck was, popped the qusetion to me: "why are diesels loud?"...I knew they had a different ignition system, but wasn't sure of the cause of the extra noise...
Now I know, and will explain to wifey, too.
Thanks again.
I finally understood some things about diesels now.
My wifey, hearing how noisy the neighbor's diesel truck was, popped the qusetion to me: "why are diesels loud?"...I knew they had a different ignition system, but wasn't sure of the cause of the extra noise...
Now I know, and will explain to wifey, too.
Thanks again.
That's Marines with a capital "M".
The passenger car diesels are much much quieter. I think VW and Mercedes Benz have done a great job. I think the TDI (or is it PDI now?) 1.9L cyl turbo is quieter than the 2.0L 4 cyl. The Mercedes E320 Diesel is soo quiet I didn't know it was diesel until I saw the badge on the back. I know BMW has them too but they don't have the guts to bring them here. I've heard a few when I was in Europe, not soo bad but not as many as the Mercs and VWs. The Liberty has a turbodiesel in it for 2005 and its a quiet one.
I just wanted to clarify a couple of things.
1. Diesels do not necessarily rev at lower rpms because of larger rotational masses. They rev low because they produce the majority of their torque at lower rpms. One of the reasons why diesel trucks last so long is because they spin at relatively lower rpms than many engines today. My 04 TDI PD Jetta has a redline of 4,600 rpm. This low redline is not limited by the engine's mass. In fact, my engine loves to rev but the redline is limited by the combustion rate of diesel fuel. My engine's design is capable of 6000 rpm but diesel fuel doesn't burn fast enough to get me there. Its not an issue since I can cruise at 110 mph all day long on long road trips through New Mexico. By the way, I am getting 46mpg cruising at 85 mph and get 750 miles per tank before I start searching for a fuel station.
2. In warm weather, my car's glow plugs never even turn on. My glow plugs turn on only in colder temps.
3. Yes diesel fuel is not as refined as gasoline. However, this lack of refinment doesn't dictate compression ignition. Any fuel will ignite with enough compression, not just diesel. Current automotive engineering efforts are underway to develop a compression ignition gasoline enigne using direct injection in order to improve efficiency by 25%. I wouldn't be surprised to see this in our near future.
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1. Diesels do not necessarily rev at lower rpms because of larger rotational masses. They rev low because they produce the majority of their torque at lower rpms. One of the reasons why diesel trucks last so long is because they spin at relatively lower rpms than many engines today. My 04 TDI PD Jetta has a redline of 4,600 rpm. This low redline is not limited by the engine's mass. In fact, my engine loves to rev but the redline is limited by the combustion rate of diesel fuel. My engine's design is capable of 6000 rpm but diesel fuel doesn't burn fast enough to get me there. Its not an issue since I can cruise at 110 mph all day long on long road trips through New Mexico. By the way, I am getting 46mpg cruising at 85 mph and get 750 miles per tank before I start searching for a fuel station.
2. In warm weather, my car's glow plugs never even turn on. My glow plugs turn on only in colder temps.
3. Yes diesel fuel is not as refined as gasoline. However, this lack of refinment doesn't dictate compression ignition. Any fuel will ignite with enough compression, not just diesel. Current automotive engineering efforts are underway to develop a compression ignition gasoline enigne using direct injection in order to improve efficiency by 25%. I wouldn't be surprised to see this in our near future.
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