One of the only grievances people have with the diesel engine is the amount of noise it creates. This has been a detriment to the diesel engine's success in the commercial passenger car world. Thankfully, there are a number of different technologies and methodologies available to reduce this drastically. The reason a diesel engine produces so much noise is that it has a special combustion process whereby the fuel is injected into the cylinder and suddenly ignited, producing a pressure wave that forms the 'diesel knock'. This knocking sound is also referred to as 'diesel clatter'. This - coupled with the fact that a diesel engine vibrates and rumbles a lot more than petrol-based engines - makes the car a lot noisier. These noise-making factors can be prevented through a number of special manufacturer's design features, by using noise-reducing oils or by modifying certain aspects of the vehicle yourself.
Engine Design Solutions
Some of the engine design solutions that have been employed in noise reduction systems in new diesel engines include a series of different methods of fuel injection, since this is where the source of most of the noise lies. Indirect injection, pilot injection, injection timing and injection rate are all factors that can be modified to produce a smooth, quiet diesel engine.
Indirect Injection
Indirect injection uses a prechamber to begin combustion off the fuel before sending it in to the main cylinder. That way the impact of the ignition is lessened and the 'diesel knock' is consequently averted. This is because oxygen is more dispersed in the main chamber and the injection pressure is lower.
Common Rail Engines
Modern common rail engines also greatly reduce noise. This is because they, using an electronic control unit, send a small amount of diesel into the compression chamber - a 'pilot' injection – just before the main injection takes place, softening the explosiveness, and consequent 'diesel knock', of the fuel's ignition. This also optimises injection timing and reduces engine vibration.
Exhaust Gas Recirculation & Turbo Boost
Since 'combustion noise' is what causes a lot of the diesel engine's noise problems by way of the 'diesel knock' and vibration, a system that affects the combustion process is going to have a chain effect reaction on the amount of noise being produced. Exhaust Gas Recirculation is a system that does exactly that. It, in a similar way to turbo boost technology, converts the engine's exhaust gas into energy to power the cylinders in the engine. Because this calls for less combustion, less 'combustion noise' will be produced overall. Vibration and harshness are also reduced by this process, as it encourages less engine use.
Can Certain Oil Help?
In terms of what you, as a diesel car owner, can do to reduce the noise of your engine, there are a number of ways that can help. Firstly, there are a range of diesel motor oils that have been specially formulated to encourage noise reduction. Shell Helix Diesel oils are an example of this. Not only does it work like regular oil and provide immediate engine clean-up until your next change, but it gives you a smoother, quieter drive too, utilising special agents in the formula.
Cetane Rating
Ensuring that you use the right fuel can help with noise reduction too. Every fuel has a cetane number which determines its ignition delay, and every engine has operating requirements. Ensuring that the fuel you use has the corresponding cetane number with your engine's operating requirements will guarantee that it runs at an optimum rate, reducing vibration and noise.
Noise Reduction Innovation
In general, there are many technologies being explored and tested to reduce noise in diesel engines. Not all of them are focused on passenger cars, but provide hope and inspiration for the basic diesel engine of the future. Perkins, a top manufacturer of petrol and diesel engines, has employed a number of methods for engine noise reduction in their products. Noise is polluting and does have an adverse effect on the environment. It's not just the irritation of car customers that is an issue, but the disruption of the world around us too. To combat the noise caused by force - combustion and engine component noise - Perkins actually modified the design of its combustion system and included a quieter front gear train to reduce overall noise. Transmission noise - the noise carried through the engine - has been stifled by installing thicker block structures around the engine. Finally, radiation - noise that 'escapes' the engine - has been treated with sound-deadening baffle plates that have been placed on the front and top engine covers.