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WHY DIESEL ENGINES ARE MORE EFFICIENT THAN PETROL ENGINE

saurabhjain

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You know that diesel engine is the most appropriate choice of the engineers when it comes to drive heavy automobile like trucks, aircraft, ships etc. But what makes it so torque, is it the engine design, working cycle or something else. Please share your  deep analysis to answer this questions

Series_40_Engine_cutaway_design.jpg

 



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Following are the reasonable points that conclude the high torque and efficiency of diesel engine.
  • Diesel engine uses simple mechanism for combustion unlike in gasoline engine. Removal of ignition system not only makes the mechanism simpler but also reduces the risk of improper combustion due to damage in ignition system. In short burning of the fuel is easy and always accessible. This results in higher efficiency diesel engine.
  • Diesel fuel is a heavier hydrocarbon in which carbon and hydrogen are strongly bonded with each other. And when energy is supplied in form of heat it gets explode releasing much higher energy then gasoline. In short diesel fuel has higher energy density then gasoline which results in huge explosion.
  • One more factor for higher efficiency in diesel engine is its property of lubrication. Although all fuel has property of lubrication but diesel fuel has much higher lubrication then gasoline fuel.
  • The compression ratio is much higher in diesel as compared to gasoline because in diesel engine air is alone compressed inside the cylinder and it’s a known fact that gas easily compresses then liquid. This is not so in gasoline engine because air-fuel mixture is compressed inside the cylinder. This higher compression gives higher heat and simultaneously higher torque.
  • We can’t use Carnot cycle to get 100% efficiency but can use its principle to attain maximize efficiency. In diesel engine heat is added at constant pressure which results in higher utilization of heat energy to get maximize work output.
These were the advantageous features of diesel engine but it has some demerits as well like it releases highly toxic gasesnoisyhigher maintenance cost and starting problem (now starting problem is eliminated by using a bulb nearby to the cylinder) to heat the engine before ignition. And it is costlierthan gasoline engine but with optimum operation and good maintenance resolve all these problems.

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6 hours ago, saurabhjain said:
Following are the reasonable points that conclude the high torque and efficiency of diesel engine.
  • Diesel engine uses simple mechanism for combustion unlike in gasoline engine. Removal of ignition system not only makes the mechanism simpler but also reduces the risk of improper combustion due to damage in ignition system. In short burning of the fuel is easy and always accessible. This results in higher efficiency diesel engine.
  • Diesel fuel is a heavier hydrocarbon in which carbon and hydrogen are strongly bonded with each other. And when energy is supplied in form of heat it gets explode releasing much higher energy then gasoline. In short diesel fuel has higher energy density then gasoline which results in huge explosion.
  • One more factor for higher efficiency in diesel engine is its property of lubrication. Although all fuel has property of lubrication but diesel fuel has much higher lubrication then gasoline fuel.
  • The compression ratio is much higher in diesel as compared to gasoline because in diesel engine air is alone compressed inside the cylinder and it’s a known fact that gas easily compresses then liquid. This is not so in gasoline engine because air-fuel mixture is compressed inside the cylinder. This higher compression gives higher heat and simultaneously higher torque.
  • We can’t use Carnot cycle to get 100% efficiency but can use its principle to attain maximize efficiency. In diesel engine heat is added at constant pressure which results in higher utilization of heat energy to get maximize work output.
These were the advantageous features of diesel engine but it has some demerits as well like it releases highly toxic gasesnoisyhigher maintenance cost and starting problem (now starting problem is eliminated by using a bulb nearby to the cylinder) to heat the engine before ignition. And it is costlierthan gasoline engine but with optimum operation and good maintenance resolve all these problems.

This is wrong.

A diesel engine utilizes the diesel cycle, whereas a petrol engine utilizes the otto cycle. The main difference between these two cycles, which are both non-ideal versions of the Carnot cycle, is their method of ignition. In the otto cycle, the combustion process is catalyzed by a spark. In the diesel cycle, the combustion process instantaneously begins when the air-fuel mixture temperature reaches the ignition temperature of the diesel fuel. A petrol engine cannot have a compression ratio as a large as a diesel engine. This is because it begins the combustion process pressure by sparking the petrol-air mixture to initiate ignition, rather than building up more pressure until ignition is initiated by reaching the ignition temperature of the petrol fuel. Thermal efficiency, which is a function of an engine's compression ratio, increases as the compression ratio increases. Though, when operating with the same compression ratio, a petrol engine is more efficient than a diesel engine, a diesel engine can have a higher efficiency than a petrol engine because it can utilize a much higher compression ratio that a petrol engine cannot possibly achieve. This is why, generally, diesel engines are more efficient than petrol engines.

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Liquid diesel does not ignite, because it is a heavier hydrocarbon. The fumes of diesel tho do. Becaue it is heavier, u input energy from the stroke in compression resulting in a slower longer lasting burn. But pound for pound petrol has more energy per unit volume than diesel. Its why its used for race engines predominantly. But the whole point is the compression. Compressing both in a piston, petrol will ignite before diesel its why sparkplugs are used in petrol and not in diesel.Everything that leads up to that compression and resulting function of engine is why its more efficient. Longer strokes, less rpm  . Hence the torque generated which is why diesel engines do a lot of work in industry and petrol is just for revving high to achieve bhp

 

http://www.engineeringtoolbox.com/fuels-higher-calorific-values-d_169.html

 

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16 hours ago, Konstantinos Oulasoglou said:

Liquid diesel does not ignite, because it is a heavier hydrocarbon. The fumes of diesel tho do. Becaue it is heavier, u input energy from the stroke in compression resulting in a slower longer lasting burn. But pound for pound petrol has more energy per unit volume than diesel. Its why its used for race engines predominantly. But the whole point is the compression. Compressing both in a piston, petrol will ignite before diesel its why sparkplugs are used in petrol and not in diesel.Everything that leads up to that compression and resulting function of engine is why its more efficient. Longer strokes, less rpm  . Hence the torque generated which is why diesel engines do a lot of work in industry and petrol is just for revving high to achieve bhp. 

you are wrong on gas having more energy per volume to simply thing we need to talk about average BTUs,

Diesel has more Btus that gasoline/petrol. Gas has 124,000 and where Diesel has 139,000 according to http://www.engineeringtoolbox.com/energy-content-d_868.html

On 10/20/2016 at 9:15 PM, saurabhjain said:
Following are the reasonable points that conclude the high torque and efficiency of diesel engine.
  • Diesel engine uses simple mechanism for combustion unlike in gasoline engine. Removal of ignition system not only makes the mechanism simpler but also reduces the risk of improper combustion due to damage in ignition system. In short burning of the fuel is easy and always accessible. This results in higher efficiency diesel engine.
  • Diesel fuel is a heavier hydrocarbon in which carbon and hydrogen are strongly bonded with each other. And when energy is supplied in form of heat it gets explode releasing much higher energy then gasoline. In short diesel fuel has higher energy density then gasoline which results in huge explosion.
  • One more factor for higher efficiency in diesel engine is its property of lubrication. Although all fuel has property of lubrication but diesel fuel has much higher lubrication then gasoline fuel.
  • The compression ratio is much higher in diesel as compared to gasoline because in diesel engine air is alone compressed inside the cylinder and it’s a known fact that gas easily compresses then liquid. This is not so in gasoline engine because air-fuel mixture is compressed inside the cylinder. This higher compression gives higher heat and simultaneously higher torque.
  • We can’t use Carnot cycle to get 100% efficiency but can use its principle to attain maximize efficiency. In diesel engine heat is added at constant pressure which results in higher utilization of heat energy to get maximize work output.
These were the advantageous features of diesel engine but it has some demerits as well like it releases highly toxic gasesnoisyhigher maintenance cost and starting problem (now starting problem is eliminated by using a bulb nearby to the cylinder) to heat the engine before ignition. And it is costlierthan gasoline engine but with optimum operation and good maintenance resolve all these problems.

I agree on the simplicity of the diesel engine, and the density, on average diesel has 139,000Btus and Gasoline/petrol has 124,000Btus

 

20 hours ago, Lava Tiger said:

This is wrong.

A diesel engine utilizes the diesel cycle, whereas a petrol engine utilizes the otto cycle. The main difference between these two cycles, which are both non-ideal versions of the Carnot cycle, is their method of ignition. In the otto cycle, the combustion process is catalyzed by a spark. In the diesel cycle, the combustion process instantaneously begins when the air-fuel mixture temperature reaches the ignition temperature of the diesel fuel. A petrol engine cannot have a compression ratio as a large as a diesel engine. This is because it begins the combustion process pressure by sparking the petrol-air mixture to initiate ignition, rather than building up more pressure until ignition is initiated by reaching the ignition temperature of the petrol fuel. Thermal efficiency, which is a function of an engine's compression ratio, increases as the compression ratio increases. Though, when operating with the same compression ratio, a petrol engine is more efficient than a diesel engine, a diesel engine can have a higher efficiency than a petrol engine because it can utilize a much higher compression ratio that a petrol engine cannot possibly achieve. This is why, generally, diesel engines are more efficient than petrol engines.

I Couldn't agree anymore on some thing,  a Diesel is 33% thermally efficient and where a Gasoline/petrol is only 25% efficient. Those are typical figures mechanically injected diesel and a carbureted gas/petrol engine. for those figures you get about 45,870Btus out of the diesel and only 31,000Btus out of the gas/petrol engine of useful work

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http://www.engineeringtoolbox.com/fuels-higher-calorific-values-d_169.html

heat of combustion is higher for gasoline than for diesel.

when i say pound for pound i mean the energy density in heat of combustion. Gasoline is higher everywhere than diesel. a more refined "better quality" fuel is higher on the scale than a more crude fuel (generally speaking). Race fuels have even higher values. 

in energy density terms gasoline is lower than diesel but this is because there is more diesel as its more dense. the actual chemical though has more stored energy than diesel does.

my original comment is not that good so let me rephrase.

there are more cycles than the otto cycle. some yield better numbers than the others depending on the fuels used and the design of the engine.

eg the IC engine we all have become used to utilizes a piston with valves, nozzles and spark plugs to provide the actual operation of the engine. it just so happens that diesel is a better fuel for this purpose than gasoline. granted you have to change a few things like the compression ratios because with gasoline if u compress it, it will burn before the chance of a stroke(compared to diesel). also diesel does not need spark plugs as you utilize the compression and ignite diesel with oxygen. 

Effieciency comes in when talking about design ( which compression is a part of) + fuel. it just so happens that in this type of engine (piston IC) it is more appropriate to use diesel instead of gasoline. this is indeed because of the compression stroke. it is thermally more efficient to compress at higher ratios and ignite (diesel) than to compress less and ignite (gasoline). but at the same compression ratio gasoline is more efficient than diesel because its a more refined better quality fuel. 

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Yeah but in the end of the day gasoline is a superior fuel where as diesel is a superior engine design. Less maintenance, no sparkplugs so less eletronics, less moving parts generally hassle free life. More torque better fuel economy. 

Also gas turbines (jets)use kerosene and it beats both diesel and gasoline simply because of the superior design 

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Yeah but in the end of the day gasoline is a superior fuel where as diesel is a superior engine design. Less maintenance, no sparkplugs so less eletronics, less moving parts generally hassle free life. More torque better fuel economy. 

Also gas turbines (jets)use kerosene and it beats both diesel and gasoline simply because of the superior design 

why is gasoline a superior fuel instead of diesel? diesel doesn't go "BAD" as fast as gasoline. also the diesel is safer for the environment

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First of all everything expires. Gasoline is a more refined fuel. It means its more pure. From diesel you get gasoline and from gasoline you get kerosene. Thats how refineries work and thats what refine means,  increase purity. Gasoline also has a lot more additives than diesel and since you are burning hydrocarbons they are all bad due to incomplete combustion which is down to design of engines not the fuel. If we could combine all the combustables exactly with oxygen you would get co2 and h2o. But we cant . Also thats where pollution, real pollution comes from, incomplete combustion and the combustion of other elements in the fuels nitrogen compounds etc. Diesel is not safer for the environmnet but neither is any fuel which u cnt burn completely. Diesel is dirtyer than gasoline and gasolene dirtier than methane. Thats why methane is the best. Its got ch4 easy to combust with o2 because of geometry of the molecule. But that also produces CO which is bad for u. And methane is the purest fuel you can get. Thats why its gas at room temperature. its always a compromise. Diesel doesnt get refined as much thats y its cheaper the only reason. Whats left of the refining process we use to build roads, bitumen. Evrything has a time place and use. 

 

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My friend look at refineries and whynthey do what they do dont worry about everything else. After the refinery its all marketing and business. Burn hydrogen with oxygen and ur pollutant is water and you get a prety good bang. Also water vapour is a pollutant it is a worse greenhouse gas than carbon dioxide. Its harmless but as a greenhouse gas its worse. The logics eh

 

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Compare SAME motors. Same ccm, without and with charder. In this case we can see, the diesel is not efficient. In same category the diesel have less power than petrol, with less consumption. But if we compare motors with same power  (in this case the diesel will be bigger) we will see the consumption will be egal. 
That is true, the Diesel do not need ignition, (but need annealing and hard start), but the injection system is more difficult and sensitive. 

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Compare SAME motors. Same ccm, without and with charder. In this case we can see, the diesel is not efficient. In same category the diesel have less power than petrol, with less consumption. But if we compare motors with same power  (in this case the diesel will be bigger) we will see the consumption will be egal. 
That is true, the Diesel do not need ignition, (but need annealing and hard start), but the injection system is more difficult and sensitive. 

that is sorta true, diesels are more efficient due to higher compression ratio, the only reason why they need to bigger, is for the emissions regulations, and the combustion pressures.

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Compression ratio sure getting a lot of attention.  Compression ratio is undoubtedly the key to peak thermal efficiency.  For many applications the throttle losses on spark ignition engines are a close second for causes of thermal loss.  

The mazda skyactive diesel has the same CR as it's spark ignition brother but has no throttling loss as well as the efficiency gains of a intercooled turbocharger system.  

It should also be noted that slow (diffusion) combustion speeds for diesels have a large negative impact on thermal efficiency (and therefor power output) at higher cycle speeds.

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Diesel engine is compression ignition engine also fuel is less volatile and ignited by compression no throttle valve rpm range of 4500 rev than petrol of 8500 rpm friction will be less ; heavier crankshaft 

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On 22/10/2016 at 7:52 PM, Konstantinos Oulasoglou said:

Yeah but in the end of the day gasoline is a superior fuel where as diesel is a superior engine design. Less maintenance, no sparkplugs so less eletronics, less moving parts generally hassle free life. More torque better fuel economy. 

Also gas turbines (jets)use kerosene and it beats both diesel and gasoline simply because of the superior design 

'less Maintenance' you are wrong dude... Diesel engine have more part than petrol engine....Diesel engine have high pressure fuel line, high pressure fuel pump, fuel filter.

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On 10/22/2016 at 7:22 AM, Konstantinos Oulasoglou said:

Yeah but in the end of the day gasoline is a superior fuel where as diesel is a superior engine design. Less maintenance, no sparkplugs so less eletronics, less moving parts generally hassle free life. More torque better fuel economy. 

Also gas turbines (jets)use kerosene and it beats both diesel and gasoline simply because of the superior design 

In my opinion, diesel fuel is best formulated to burn in diesel engines (compression ignition) and gasoline is best formulated to burn in gasoline engines (spark ignition). Efficiency is directly proportional to the amount of the fuel that is actually burned to contribute to the power stroke of the engine. This amount of fuel is directly proportional to the amount of fuel in gas form at the time of ignition. Any portion of the fuel that is in liquid form will not burn and come out of the exhaust as particulates and un-burned hydrocarbons. So, in answering the original question, I don't agree with the premise of the question. I don't agree that (in general) diesel engines are more efficient than gasoline engines. It is all a function of atomization and the amount of fuel in gas form available for combustion during the power stroke.

That being said, in the compression ignition engine, more fuel becomes gas the higher the compression ratio goes.

BTW. gas turbines, depending on their configuration, can burn a very wide range of fuels from gases as light as hydrogen, methane, propane to liquids as kerosene, naphtha,  diesel, No.2 fuel oil, all the way to heavy No. 6 fuel oil. The choice of fuels depends on a wide variety of factors like price/availability of fuel, emissions constraints and efficiency requirements. Here again, the efficiency of the gas turbine depends on the amount of the fuel that is actually burned to contribute to the combustion process. Another factor that largely contributes to the efficiency of a gas turbine is the efficiency of the compressor section.

 

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Compression Ratio is main difference between Petrol and Diesel engine. 

Self-ignition in Diesel engine. Therefore Diesel engines didn't cause knocking Effect. That's the Economical point.

Diesel engine have high amount of torque than Petrol engine.

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Diesel engines are superior designs to cancell out high vibration due to high compression ratio resulting to higher power stroke n efficient turque power than gasoline engines.dont know much though but I like this forum learnt much

But how do u know a good diesel fuel

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Diesel engine is combustion ignition and a petrol one is spark ignition

As we know for a small petrol engine we require 10000 volts approximately to generate a spark in petrol and extend the Piston towards bdc

Coming to the discussion, I feel for a massive engine which is used in ships the size of cylinder is more which is also an increase in clearance volume where combustion takes place . This is when compared to small automobile engineering.

We can't include a spark ignition system of huge voltage in these big engines because it increases complex mechanisms

Morover if we use a diesel engine no need of carburetor because air is drawn directly

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Diesel engine has high compression ratio as compared to petrol engine....

According to Relationship between efficiency and compression ration as described in formula "Engine having higher compression ratio has more efficiency as compared to engine having lower compression ratio...

 

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