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Old 28th March 2010, 12:57   #121
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The Diesel engine, being heavier and more sturdy, takes a tad longer than a gas engine to reach its ambient operating temperature. How long, I do not know. But I would say run it at least 10 KM in a single go-
I also read similar thing in some technical journal. But it was not 10 km but it was about 5-7 km. For the petrol engine, it was about 2 km.
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Old 29th March 2010, 10:51   #122
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I'm not sure how accurate that statement is, though it is probable. My Jeep & Indigo surely take longer to reach the optimum temperature level (4 - 5 kms for the former, about 2 - 3 for the latter). On the other hand, the C220 does so in less than a km.
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Old 29th March 2010, 11:12   #123
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1 - Is is to negate the advantage of being more fuel efficient and the fact that diesel is available cheaper than petrol?
No, the inherent cost of producing a diesel is higher (for a few companies) as compared to petrols as the overall sales of the same are lower. The newer technologies add to the costs of the engines as they are add on's to the older engine technologies. Most of the manufacturers started off by adding the CRDI technology to their existing engines and then have been further refined over the years. The newer technology means a greater licensing cost that gets passed on to the end consumer.


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2 - Is it that making a diesel heart (Engine) costs more?
Yes it does, but if you compare it to a turbo petrol, NO. hence it would depend to what type of engine that you are comparing to.


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3 - The manufacturers are just charging a premium for the economic benifit that diesel cars bring in to end users in India?
Not true, in certain cases the diesel engine being produced here in India is typically larger (cc capacity) than the petrols for an equivalent power output hence the prices being higher.


Not to forget the idiotic taxation policies that the government has towards vehicles and fuels, the overall cost to own and run a diesel is a lot lower than most other countries in the world.
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Old 18th February 2011, 21:57   #124
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Post Re: The Technical Truth? :Petrol vs Diesel

I dont know what i am missing here but here's my take on this. Petrol engines run on the Spark ignition system and diesel engines run on compression ignition. In spark ignition system, the fuel air mixture enters the cylinder(intake stroke), is compressed(compression stroke), the spark plug ignites the compressed mixture and expands, resulting in work done(power stroke), this is followed by the exhaust stroke wherein the combustion products are let out preparing the engine for the next cycle to repeat.

In compression ignition system, there is no spark plug. During the intake stroke, air enters the cylinder, is compressed during the compression stroke, and high pressure diesel is injected in the form of a fine spray, this causes spontaneous combustion and results in works done.
The pressures the engine is subjected to in diesel engines is much higher than those in the petrol engine, hence diesel engines have to withstand higher pressure than petrol engines. For this reason the diesel engines have to be of robust construction, resulting in heavier engines.

Coupled to this, the fuel injectors should be capable to withstanding /sustaining high fuel pressure in order to initiate combustion. For this very reason, the fuel that enters the fuel injectors should be, in every sense free from all dirt/sludge particles. I am not sure about the construction/layout of diesel engines, but i believe it would require some sort of filter between the tank and the fuel pump(i need citations for this fact about car engines, as i know marine diesel engines require a complicated fuel/lube system). And because these engines run on diesel, the lubricating engine(engine oil) has to be of a higher grade, to carry out partial cooling. All this couples to higher cost of diesel engines.

Now, moderators, i did not know where to post this, so please move this if required. I have a query regarding the working of diesel engines, giving specific regard to turbocharger.
1. Are all diesel engines turbocharged?
2. Is the turbocharger driven by exhaust gases? If so, when does the turbocharger kick in?
On 2 stroke marine engines, at lower RPMs, we have an auxiliary blower supplying air to the engine. As the engine picks up speed the turbocharger, driven by exhaust gases, kicks in, sucking air from the atmosphere. This air that is sucked in has to be cooled, does this also apply to car diesel engines?

Anyone, please reply.
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Old 23rd February 2011, 21:50   #125
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Default Re: The Technical Truth? :Petrol vs Diesel

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Originally Posted by saurabhkanchan View Post
Now, moderators, i did not know where to post this, so please move this if required. I have a query regarding the working of diesel engines, giving specific regard to turbocharger.
1. Are all diesel engines turbocharged?
2. Is the turbocharger driven by exhaust gases? If so, when does the turbocharger kick in?
On 2 stroke marine engines, at lower RPMs, we have an auxiliary blower supplying air to the engine. As the engine picks up speed the turbocharger, driven by exhaust gases, kicks in, sucking air from the atmosphere. This air that is sucked in has to be cooled, does this also apply to car diesel engines?

Anyone, please reply.
Hi,
Automotive diesels are four strokes, not two strokes. Will start on its own.

Difficult to meet todays emission norms without a turbocharger.

In common usage, a turbocharger (actually a turbine powered supercharger) is exhaust gas driven. And yes, thats what used in autos. When it will start working (the turbo kick) depends on design decisions.

Yes, intercoolers are used.

Regards
Sutripta
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Old 25th February 2011, 12:04   #126
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Default Re: The Technical Truth? :Petrol vs Diesel

In modern diesel engines, in order to meet most emission requirements and the refinement levels, the engine design and manufacturing costs are much higher. Compared to petrol MPFi engines which require pressurised fuel at about 3-4 bar, Common rail diesel engines require the injection pressures in the range of 1500bar for regular injectors and even crosses 2000bar for piezo injectors! Moreover, the petrol injectors have constant lift and the amount of fuel injected is controlled by the duration of injection. Diesel injection systems do not have this luxury as the window of injection is too small and the quantity is governed by the pressure and variable lift in the injector. this results in a much more complicated design for the injectors and the cost difference is HUGE.

In order to supply the fuel at such high pressures, the fuel pumps for such engines are also extremely expensive along with the fuel filter.

Most modern common rail engines are turbocharged which adds to the cost. Some even come with VGTs to minimise turbo lag which are even more expensive. Turbos or superchargers are still relatively uncommon in the road cars (not talking about the high performance sports cars here).

Add to that EGR systems and more expensive exhaust treatment systems for diesel engines you end up having a significantly more expensive engine under your hood.

Saurabh, to answer your questions, yes - most modern diesel cars do have turbocharges and a significant number of those are coupled to an intercooler as well. Modern emission norms and the customer expectations from an engine make it difficult for a manufacturer to sell diesel cars without Turbos.

The turbos kick in at different engine speeds in different vehicles. The idea behind it is that the exhaust energy should be sufficient to turn the turbine fast enough to generate enough boost. These exhaust energies are higher at higher engine speeds that is why when driving diesel engines, you feel that extra punch when you reach a particular RPM. This delay is minimised in case of VGTs
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Old 1st March 2011, 14:46   #127
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Default Re: The Technical Truth? :Petrol vs Diesel

sutripta, niteshbids thanks for your replies. Can you please clarify the following also?

Because the turbochargers are exhaust driven, the turbine may get deposited with carbon particles from the exhaust, which can lead to an imbalance with the blower and hence may affect the engine performance. How is this taken care of? What is the frequency of turbocharger cleaning?

how is the turbocharger bearing lubricated? Can anyone give me line diagrams for the fuel, lube and cooling systems for 4 strokes, mentioning the pressure an temperature range at various points?

What is the temperature range for air inlet at the turbocharger and to what temperature does the intercooler bring it down? What is the cooling medium used in Diesels, both for engine and turcocharger?
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Old 1st March 2011, 20:10   #128
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Default Re: The Technical Truth? :Petrol vs Diesel

^^^
Hi,
If we start as the base, the older (non CRDI) auto engines, these are similar to your Yanmars and Daihatsus. (Except these are normally IDIs. And running on HSD.) How often do you clean the turbos of those?

Bearing lubrication is always problematic, esp in a variable speed engine. Normally taken from the main oil gallery. And with a restrictor pin. Some people used to throw away the pin and put in a filter.

I'm sure others will reply with more specific facts and figures. (Else I'll have to wade through a lot of dust to find some of my old books. And those would be totally out of date.)

Regards
Sutripta
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Old 1st March 2011, 20:46   #129
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Default Re: The Technical Truth? :Petrol vs Diesel

thanks for you inputs sutripta

cleaning of turbochargers on marine engines are primarily based on running hours. coupled to it that fact that these run on H.F.O. cleaningoverhaul interval is also based on condition monitoring but is specified by the manufacturer.

does the turbocharger lube oil need cooling once its been through the system? iif so how is it cooled again?
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Old 2nd March 2011, 09:39   #130
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Originally Posted by saurabhkanchan View Post
sutripta, niteshbids thanks for your replies. Can you please clarify the following also?

Because the turbochargers are exhaust driven, the turbine may get deposited with carbon particles from the exhaust, which can lead to an imbalance with the blower and hence may affect the engine performance. How is this taken care of? What is the frequency of turbocharger cleaning?

how is the turbocharger bearing lubricated? Can anyone give me line diagrams for the fuel, lube and cooling systems for 4 strokes, mentioning the pressure an temperature range at various points?

What is the temperature range for air inlet at the turbocharger and to what temperature does the intercooler bring it down? What is the cooling medium used in Diesels, both for engine and turcocharger?
hi Saurabh,

regarding the particle deposition and requirements of cleaning (if any) i'll have to check it out with my colleagues who would be able to clarify things for me too. But I'm sure of the fact that turbos in gasoline engines (which are also driven by exhaust) do not require any kind of maintenance.

For the lubrication of the turbocharger, there is an oil inlet at the turbo which is fed through the main engine oil pump and the oil drains back to the engine oil sump.

The inlet air temp at the turbo is a little bit over the ambient temperature. It's the temp at the outlet of the turbo that is quite high (70-75 degrees) (partly due to the compression and partly due to the fact that the turbo runs extremely hot). A well designed intercooler in my opinion would bring down the temperatures to the vicinity of 55-60 degrees. these figures are quite dependent on theambient. the higher the ambient, these figures would be higher.


The cooling arrangements for the diesel engines are similar to the gasoline engines. maybe small changes in details but the general idea is still the same. there is no cooling arrangement for the turbo itself because cooling down the turbo would mean lowering of the exhaust energy and thus the turbo efficiency.

update to my last post (had to post separately as my earlier post is still under moderation)

There is no requirement to have any kind of maintenance operation on turbos. The turbos are designed for such conditions and are basically fit it-forget it components.

The oil for cooling the turbo is shared from the engine as i said in my last post, so no special cooling requirement for that oil. fresh oil is fed from the engine oil pump (which is also feeding oil to all other parts of the engine like the valve train etc) and drains back to the engine oil sump.

Note from the Team-BHP Support Team : Please use the "edit" button if posting within 20 minutes of the first post, instead of creating another back-to-back post.

Also use "Multi Quote" option for quoting Multiple posts.

Last edited by n_aditya : 2nd March 2011 at 15:00. Reason: posts merged
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Old 2nd March 2011, 10:27   #131
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Default Re: The Technical Truth? :Petrol vs Diesel

niteshbids those are valuable inputs, thanks a lot.

can you also help me with the line diagram of various systems in the vehicle: fuel, lube and cooling?
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Old 2nd March 2011, 12:51   #132
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Default Re: The Technical Truth? :Petrol vs Diesel

Here is a picture of the fuel system for a common rail diesel engine. I'll have to dig a little deeper or work on a line diagram myself. Gimme some time for that.
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Old 2nd March 2011, 13:25   #133
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Here is a picture of the fuel system for a common rail diesel engine. I'll have to dig a little deeper or work on a line diagram myself. Gimme some time for that.
i cant thank you enough for whatever inputs you are providing and i apologise for the trouble i am putting you through.

Please let it keep coming, your inputs are a great help to me. what is the f.o pressure at the time of injection? I had over heard a scorpio owner complaining that the overflow tank had got punctured, do diesels have a separate d.o overflow tank?
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Old 2nd March 2011, 14:01   #134
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Default Re: The Technical Truth? :Petrol vs Diesel

You're most welcome buddy. I really enjoy contributing to such threads and queries so you really don't have to apologize for anything here.

I'm not sure what overflow tank you are referring to here as am not aware of any overflow tank for fuel. Also, if you could clarify what you mean by the f.o pressure, i'd be able to help you with that.
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Old 2nd March 2011, 15:58   #135
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. Also, if you could clarify what you mean by the f.o pressure, i'd be able to help you with that.
f.o- fuel oil pressure,

overflow tank- not all of the diesel entering the injectors would go into the cylinder for combustion. some part would return to the fuel tank, illustrated in the picture you posted by a return line from injector to the fuel tank. I am not sure if automotive diesels have an overflow tank separately, but on enquiring with the scorpio owner, he mentioned a separate tank for overflow.
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