Diesel technology is very well known for is durability, reliability, and overall ruggedness as applied to the trucking, construction, mining, and general power industries. Without question, the acceptance and general economics of diesels have proven themselves time and again as the power source of choice. However, as the markets and overall populations of diesels grew so did public awareness of the smell, sight and noise associated with them. Not so long ago it was common place to see a 12-wheeler roaring down a highway belching black smoke.
Technology needed a boost and industry addressed it mostly due to over the road emissions requirements promulgated in the 1970’s. Initially, diesel engine manufacturers balked at the requirement to reduce NOx and particulate and cries of ‘it can’t be done with today’s technology’ ensued. Engineers quietly went to work on combustion development to gain a better understanding of what fuel characteristics had the biggest impact on NOx formation and particulate matter. There was little doubt that something was going to happen about stack output. The prime concern was as you get better with one attribute the other worsens as the two traits are inversely proportional. Regardless, there was no doubt that increases in injection pressure and relative impacts to fuel droplet size were beneficial, so the call was put out to industry for 1000 Bar injection pressures.
In the day, pump-line nozzle systems held a large portion of the market with engines in the 6-12-liter category for trucks. As the mid 80’s approached reliable injection technology of 1000 Bar was developed and implemented which aided in achieving 10.7 g/bhp.hr, but on the horizon was further reduction to 6 and 5 g/bhp.hr NOx and much lower particulate to .25 and .10 PM.
Injection pressure levels continued to increase, and rate shaping became a larger need. Manufacturers realized that by controlling the rate that fuel is introduced into a cylinder, you can tailor the combustion event and ultimately the chemical release of emissions. Not only did this help achieve required emissions standards but side benefits of quieter operation and easier cold starts emerged. Things were looking up.
The prime hurdle, however, was that the technology of the day was not easily converted to achieve very high injection pressure, rate control and the ability to convert to digital fuel controls and total vehicle integration. It was this impasse that started the development of rail technology in earnest.
Engineers knew that using an injector right at the cylinder was a very economical way of controlling combustion. Unit injection has already been used for decades with mechanical systems and proved to be a reliable alternative to pump line nozzle technology. But as with all systems, rate control and digital enhancement of injection control needed one element that was yet to be developed. A reliable solenoid.
Simply put, delivery of very high fuel pressures (1800 Bar and beyond) was achievable, all you needed was something to start and stop the injection event. If you could control how that start and stop happened digitally, you could vary your injection for each application. Suddenly, a vision was getting solidified. An enhanced solenoid was the device to be implemented to achieve that desired result.
Ultimately solenoids with good durability, little hysteresis and economical manufacture hit the market. Fuel system manufactures scrambled to gain acceptance and deal with the emotions of high-pressure rail or low-pressure rail and interchangeability. Ultimately, it was up to the vehicle manufactures to achieve the required emissions levels, therefore, the evolution of what is now very commonplace in the industry transpired.
Certainly, there are many books written about diesel development. Low-sulfur fuels, particulate traps, Urea injection, EGR etc. all play a role in modern engines but suffice to say, none of this would have happened without the development and evolution of the fuel management required as the heart of the technological enhancements.