Diesel generators are available in a huge range of sizes, all the way from 10 kVa to several megawatts. They are normally installed in buildings or containers, therefore each application comes with unique space constraints. For these reasons, Blackthorn treats every order for an exhaust after- treatment system for a generator as a separate project, with all major parts ‘made to measure’ rather than ‘off the shelf’.
This approach was essential when designing and supplying exhaust systems for four Cat C32 generators which were being installed in Lebanon.
The customer required diesel oxidation catalytic converters (DOCs) to reduce emissions, and silencers to reduce the noise.
In the case of the DOCs, the customer asked for the substrates to be removable, so that they could be taken out for cleaning or replacement. However, a low ceiling height in the building meant that they could only be taken out horizontally rather than vertically, therefore the housing needed to be designed to permit this. It was also necessary to ensure that it was easy to install and remove the substrates whilst, once installed, they didn’t rattle.
After referring to the specification sheet of the engine, Blackthorn calculated that substrates with a diameter of 500mm, length of 90mm and 200 cells per square inch would achieve the customer’s target emission levels, whilst also keeping within the exhaust backpressure limit of the engine. The substrates were made from fecralloy which was vacuum-brazed together, then coated with a proprietary slurry washcoat and precious metals.
In addition to the catalytic converters, the customer also requested Blackthorn to supply silencers capable of an attenuation of 28 dBA. As Blackthorn does not have in-house expertise in acoustics, they turned to a consultant for help with this, and supplied him with acoustic data obtained from Caterpillar, as well as the space constraints. The consultant used his silencer design software to come up with a design for a reactive silencer which met all the parameters. This was an essential exercise since the noise spectra of every model of engine is different, and reactive silencers need to be ‘tuned’ to the wavelength of the sound waves emitted by the engine. Acoustics is a very mathematical discipline, but with modern computing power an expert can design a silencer for a specific application fairly quickly, so there is no excuse for using so-called ‘universal’ silencers.
Once fabricated according to the drawings, the catalytic converter housings and silencers were powder coated then, once the catalytic converters had been installed, they were packed into bespoke wooden crates before being containerised and shipped to the customer.