Equipment World

August 2015

Equipment World Digital Magazine

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W hile NASA may have sent a probe all the way to Pluto, there's another engi- neering miracle sitting right here on earth largely unnoticed under everybody's noses. We're talking about the modern era Tier 4 Final diesel engines that use high pressure common rail fuel systems and electronically actuated injectors governed by a electronic control module (ECM). These systems can put small, rapid-fi re bursts of fuel into the cylinders at rates in some cases of more than 6,000 times a minute. As a result, today's big diesel engines can produce more power with less fuel than ever before while simul- taneously cutting exhaust emissions by more than 95 percent. To give you a better idea of how these modern miracles of engi- neering work we talked with Jim Fier, vice president of engineer- ing at Cummins and Ilidio Serra, manager technical service support, Robert Bosch automotive aftermar- ket division. We start by looking at the differ- ence between the older style injec- tors and today's new technology. MECHANICAL INJECTION Prior to modern emissions regula- tions most diesel engines relied on mechanical fuel injection – a cam- shaft lobe pushing against a roller tappet drove a plunger that pres- surized the fuel. In these systems, pressurized fuel travels through a line until it hits a spring on the injector and forces it open, allowing the fuel to fl ow into the cylinder. Pressures up to 15,000 psi were possible, but only one injection per rotation of the cam lobe and one shot of fuel per combustion cycle were possible. Mechanical fuel injection is simple and reliable. It's still used on lower horsepower engines, but it can't provide the precise control, emis- sions reductions and broad power range needed for today's larger Tier EquipmentWorld.com | August 2015 67 maintenance | by Tom Jackson | TJackson@randallreilly.com HOW DIESEL GOT ITS GROOVE BACK: HIGH PRESSURE COMMON RAIL AND ELECTRONIC FUEL INJECTION COMMON RAIL FUEL PUMP INJECTORS The common rail delivers high pressure fuel to the injectors, freeing the injectors to fi re much more frequently than the mechanical cycling of the engine would allow. Source: Cummins MECHANICAL INJECTION

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