Equipment World Digital Magazine
Issue link: http://read.dmtmag.com/i/548484
4 Final engines, primarily those 74 horsepower and up. As emissions regulations grew increasingly strict, improvements evolved, including distributor pumps, in-line pumps and unit in- jectors, eventually taking pressures up to 23,000 to 26,000 psi. Many OEMs were able to get through the Tier 3 emissions requirements using these more sophisticated systems. But the real miracle didn't happen until the introduction of high pressure common rail fuel systems (HPCR), which enabled injection pressures up to as much as 36,000 psi. COMMON RAIL SYSTEM In a HPCR system, the injectors draw their fuel from a single accu- mulator-like rail that serves all the injectors with a common source of fuel. The fuel stored in the common rail is pressurized, up to 30,000+ psi, while waiting to be used. The advantage here is that you are no longer depending on a cam lobe or fuel pump to pressurize the fuel at the injector. The tasks of pressurization and injection, which are linked in mechani- cal systems, become independent. And the higher the pressure, the better the fuel atomizes once it is sprayed into the cylinder. Instead of the speed of the cam or the fuel pump determin- ing when the injector opens and closes, an HPCR system con- trols the injector with a small, rapid fi ring actuator, either a solenoid or piezo crystal built into the injector. And because they are electronically actuated, they can fi re as fast as you can turn an electric currrent on and off. These electronically governed injectors provide much better control of injection timing and quantity compared to mechanical systems, says Fier. "This has been a signifi cant enabler of designing cleaner and more fuel effi cient diesel engines," he says. MULTIPLE INJECTION EVENTS "Combustion in a diesel engine is much like the recipe for baking a cake," says Serra. "If you measure your ingredients correctly, have the right temperature settings and time, you get a perfect cake every time." The challenge is that the recipe may change from one second to the next. Every time you drop into a different gear, climb a hill or pour on the throttle to maxi- mize breakout force, the mix of pressures, temperatures, injec- tion events and timing changes the recipe. Only common rail systems with ECM brains and ultra-fast, electronically-controlled injectors have the speed and versatility to respond to these changes and still August 2015 | EquipmentWorld.com 68 maintenance | continued In a mechanical fuel injection system, pres- surization of the fuel and injection timing depends on the rotation of a camshaft tied to the reciprocating action of the engine. NOZZLE BODY Source: Bosch Automotive Aftermarket