CrazyEngineers Archive
Old, but evergreen and popular discussions on CrazyEngineers, presented to you in read-only mode.
@Kaustubh Katdare • 02 Aug, 2013
Those of you who've driven the diesel and petrol vehicles will know that the diesel engines vibrate a lot. In fact, it's a problem that's not been solved even in the most modern cars. From what I learned by reading online is that the vibrations in diesel engine is an outcome of the heavy compressions going on inside the diesel engine.

I also read that problematic engine mounts added to the problem but that's been solved to a greater extent these days.

Do you have any suggestions to fix the problem and make the diesel cars run just as smooth as petrol counterparts?
@zaveri • 03 Aug, 2013 • 1 like The one solution i suggest is to mount the engine on compression springs or use some kind on vibration damping material such as rubber at the mounting points.
@Kaustubh Katdare • 03 Aug, 2013 zaveri : That looks like the most logical step to take. Obviously there seem to be a few shortcomings with that approach. What are those, I'm not sure but that would have made it to the production vehicles by now.
@zaveri • 03 Aug, 2013 • 1 like
Kaustubh Katdare
zaveri : That looks like the most logical step to take. Obviously there seem to be a few shortcomings with that approach. What are those, I'm not sure but that would have made it to the production vehicles by now.

The engines used for non-automobile applications such as for pumps are generally mounted on 3 or 4 conical compression springs.

i am not sure why exactly this method is not applied in the case of automobile engines. My assumption is that the besides the engine, the rest of the vehicle also creates vibrations, as it moves on the road. and these vibrations in some way affect the spring loaded engine, and this may complicate the design.

i wonder what the experts have to say. tagging CE Designer
@zaveri • 03 Aug, 2013 Petrol engines are made of aluminum or cast iron.

now cast iron has good vibration damping properties, and therefore you dont get vibration problems with petrol engines.

cast iron cannot be used for diesel engines, because it cannot withstand, the pressure created due to combustion.

the solution may lie in finding a material which can damp vibrations and also withstand the pressures.
@CE Designer • 05 Aug, 2013 • 2 likes I would agree with zaveri 's suggestion w.r.t. the engine mounts. My recommendation would be to construct a mounting frame and install vibration dampers (oil damper) at each mounting point. My belief is that the regular rubber mounts do not absorb most of the shock but transfers it to the chassis of the vehicle. The oil dampeners/shock absorbs are simple. These are the same shock absorbers for your tires, I just recommend mimicking a smaller version for the engine mounts. Some shock absorbers use air and some use oil.
Just by the way, associated with vibration is the noise as well. Engine vibration also causes other body parts to rattle causing noise.
@CE Designer • 05 Aug, 2013 Oil dampers are used on large bridges and high rise buildings to absorb shock and wind/weather forces. Why cant we use smaller versions for an engine?
@CE Designer • 05 Aug, 2013 Diesel engine driven generator and pump units are supposed to be mounted on a special surface made of a special material. Grout is usually used to prepare the foundation and base because grout absorbs shock and vibration. Regular concrete cracks and breaks apart.
@Sarathkumar Chandrasekaran • 06 Aug, 2013 The main disadvantage is its size.Diesel engine occupies more space because of its parts such as fuel injector,fuel pump,air cleaner,etc.As diesel engine works on compression it often leads to vibration of engine and as our friend said use of dampers and position of engine plays a big role here.
@Gurjap • 07 Aug, 2013 Actually, a whole lot of Diesel engines you'll see (made in India variety, sometimes found in auto rickshaws, or in tractors , or Engine Testing Labs of govt engineering institutions) are made of CI (cast iron), and CI most definitely can withstand the kind of loading a Diesel system will produce. The matter of high vibration is not so much the material of the engine as it is the inherent working of the Diesel engine.

As Kaustubh rightly points out, higher compression ratio has something to do with it. But consider also, how exactly a Diesel Engine works. As compared to a SI system in gasoline engines, where the spark plug produces a flamefront that travels down in charge, the compression ignition system is designed to almost-detonate the whole fuel almost instantaneously. This is why in order to smooth out the power production, Diesel is sprayed in the chamber even as all the diesel droplets present previously are self-igniting simultaneously.

So at one hand we have a system that initiates a more laid-back ignition, to a more impulsive one. As you can rightly imagine, the latter produces more vibration.
@Ramani Aswath • 08 Aug, 2013 Diesel engines work on compression ignition, petrol ones on spark. This requires a higher compression ratio in diesels. Over damping has issues related to the mechanical transmission system. Stationary diesels have the load directly coupled and are an integral unit. This allows the entire system to be mounted suitably.
@Kaustubh Katdare • 08 Aug, 2013 How about using Rubber or spring mounts? Or - how about an anti-damping system that would use hydraulics to nullify the vibrations? I think it'd make the costs go up high.
@Ramani Aswath • 08 Aug, 2013 The engine vibrations can be controlled. The trouble is caused by the mechanical links in the total transmission.
@Gurjap • 08 Aug, 2013 All these methods that Kaustubh points out are being used in defense applications where their costs are justified. More specifically, they are used in Diesel Electric submarines.
@Siddhant Mukherjee • 29 Aug, 2013 Most engines use a slider crank mechanism but if you analyse the mechanism you will find that how well you try you can never balance the system completely. So, different engine orientations such as V, W, Flat exist so as to minimize the vibrations due to jerk produced by reciprocating piston. Apart from this the firing order of cylinders is also a way to reduce vibrations. Now that's about the vibration of mechanism but what about the variable pressure created inside the engine during compression, ignition etc. These variations in pressure result in varying torque on your drive system which also results in vibration. Diesel engines experience these vibrations at a magnified level due to higher compression ratio. A way to reduce such vibrations is to employ a heavier flywheel but remember a heavier flywheel will mean heavier drive shaft and increase in weight resulting in loss of performance of your engine.
@Sarathkumar Chandrasekaran • 30 Aug, 2013 I also want to know whether there is any chance of decreasing vibration by choosing a certain type of engine.(An V type or W type or opposed piston or radial engine)
please reply so that this discussion continues.
@Siddhant Mukherjee • 30 Aug, 2013 Yes, the arrangement of cylinders and their firing order are the most important criteria for balancing your engine apart from the balancing weight you use with the crank.
In fact, if you use a flat or boxer engine you experience the minimum vibration due to your mechanism but space becomes a major constraint there. Subaru impreza uses a flat engine.
@lal • 30 Aug, 2013 I was thinking about introducing a better damping for the 'body' rather than the engine itself. Engine can't be damped beyond a certain extent because of the mechanical power transfer links all around as mentioned in the posts above.

But there isn't any limitations like that for the vehicle body, except the mechanical strength needed to bind it to the chassis. I was wondering if there would be a better damping option possible in the way a body is bound to the vehicle chassis.
@Siddhant Mukherjee • 30 Aug, 2013 • 1 like @lal: Yes, you are correct and therefore today most of the cars use monocoque chassis and not ladder. Apart from this, if we look at the best cars today, the body dynamics is much more developed than whatever we are discussing here. Active dampers in suspension, Electronic stability control and many more such technologies help to give you a very comfortable ride. But you need to empty your wallet for that. In fact your seats are also a damper imagine yourself sitting in a car with wooden seats. The thing lies the fact that each and every system is a spring and damper. you need to choose such materials which act more like a damper for restraining vibrations.
@Sarathkumar Chandrasekaran • 31 Aug, 2013 I know i am little off the topic but here is my perception If we talk about the suspension, damping, etc dont forget about the tyres.From my point of view TyresT have the best suspension powers.It is the first thing that face vibration and it transmitts the vibration to the body.So if we can control the vibration in tyre itself there are huge chances of damping vibrations.tyres also had evolved a lot and and now we see there is a possibility of absorbing maximum efficiency from the vehicle.
@Siddhant Mukherjee • 01 Sep, 2013 @CSK AUTO : I agree that the tyres are also a source of damping and as I mentioned earlier, each system is a spring and damper system with different capabilities of damping. You need to choose materials at different portions of vehicle in accordance with your needs that whether the part needs a higher value of springing or damping. And lets me remind you not only the bumps in the road but your engine is also a major source of vibration and in fact any varying force is a vibration and in any vehicle you always deal with varying things.

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