Whether in a pickup truck, semi tractor or motor coach, we are all used to hearing the sound of a diesel engine, knocking loudly like a herd of knock kneed cattle on a slow gallop. But have you noticed that newer diesel equipped vehicles are getting quieter and quieter? European diesel powered automobiles are extremely quiet and can not, in many cases, be differentiated from the sound of a gasoline car. So much so, that one could actually mistake a diesel as a gas when filling the tank – not once, but twice. Please don’t ask me how I know. Suffice to say, there is an auto rental company in Italy that will only rent me a gas powered ride.
So, to what technology do we owe this reduction? Sound proofing? Smaller engines? Less fuel delivery? No! The main contributor to the smoother and quieter diesel engine is in the combustion chambers, the electronic control module program, and fuel injection design changes. The cylinder heads and piston faces are designed to take advantage of even fuel mist dispersion and pre-combustion type chambers. (Note: If you do not see the pictures, please click on the heading for the full article)
The electronic control module, (ECM) as well as many other tasks, monitors the fuel mixture and manages the operation of the direct fuel injection. Unlike the cam lobe operated mechanical injection system, the modern electronic common rail injection is capable of multi injection events per cycle. Additionally, the common rail design employs extremely high pressure fuel delivery. The use of this high pressure ensures far better atomization of the fuel mixture.
The loud knock sound we are accustomed to hearing is caused by the explosion within the high pressure combustion chamber during the fuel injection. Today, the electronic controlled injection creates a very small injection just prior to the firing stroke and main metered injection. This pre-injection is called a Pilot Injection, and starts a low powered burn prior to the full delivery at the power stroke. This substantially reduces the explosion shock while still retaining the same energy. To increase the energy push on the piston, the injectors deliver mini squirts of fuel during the piston’s travel downward on some designs, which further enhances the engine’s smoothness and quietness.
North American diesel vehicles are fast catching up with Europe’s lead in this field. General Motors, for one, has a new Duramax engine design scheduled to be introduced in 2010, (shown in photo above) which promises major advancements. These advancements will obviously deal with fuel mileage and will be environmental air and sound friendly.
This sound reduction in modern diesel engines is particularly beneficial to the recreational vehicle market. This is because so often, during early morning departures, these vehicles are in close proximity to other rigs containing people that may be sleeping. Additionally, it makes it easier for a spotter to communicate with the driver during back in procedures.
So, the future might bring an end, or certainly a reduction, to waking up to that harmonious mechanical clatter heard as a tow vehicle or motor home prepares for departure. Both diesel and gas owners will have something to rejoice.
With Some Quieting Thoughts – Lug_Nut – Peter Mercer