You can always tell a diesel truck is headed your way from the "diesel rattle," right? Well, not so much anymore. Significant technological advances have eliminated much of the rattle we associate with older diesels. Today's new generation of light-duty diesels has been transformed into vehicles that are nearly as quiet as automobiles powered by conventional gasoline engines.
What has changed? New and improved diesel-system technologies like common-rail injection allow the use of electronic fuel-management controls, one of the primary advances that has quieted the diesel. Developed primarily by firms such as Robert Bosch and Siemens, these systems are in use in new light- and medium-duty diesel automobiles and light trucks around the world. The common-rail system (and other new-generation diesel systems) allows fuel to be injected in multiple pulses into the engine combustion chambers during each injection cycle instead of one large pulse. The multiple injections soften the normally steep pressure rise in the combustion chamber, which was responsible for the rattle in older diesel cars and light trucks.
Bosch, the world leader in diesel fuel and engine-management systems, provides advanced diesel components and systems for millions of automobiles and trucks. Bosch has been a major player in diesel-injection components since making the diesel engine as we know it viable by introducing the first series-production, inline, fuel-injection pump in 1927.
State-of-the-art injection engineering transforms diesel engines into economical, silent, and high-torque drive systems. The latest-generation common-rail diesel system, for example, effectively lowers the exhaust emissions of diesel engines by up to 20 percent in comparison to previous generations and alternatively increases the achievable engine output, reduces fuel consumption, and lowers engine noise. A special feature in the third generation of Bosch's common rail is the rapid-switching piezo injectors.
Diesel engines compress air in the cylinders to as much as 20:1 (or higher) compression ratios, while the normal gasoline internal-combustion engine compression ratio is usually around 10:1. The extreme compression makes the air very hot, and when fuel is injected into this hot, compressed air, combustion occurs.
In older-generation diesel engines, pressure buildup from the pump in the fuel lines opened spring-loaded injection valves at about 5,000 psi. The sudden injection of fuel into the cylinder caused a steep pressure rise to suddenly build in the cylinder and combustion chamber. Sounding much like a series of small explosions, these were heard as diesel rattle. The use of pre-injection pulses and "shaping" the main pulse in today's diesel lessens the sudden pressure rise-and the diesel rattle.
The higher pressures (over 26,000 psi and climbing) currently utilized by the new electronically controlled common-rail systems allow the injectors to deliver a finer atomization in the injected fuel, which improves combustion efficiency while reducing particulate emissions.
Today's diesels are more sophisticated than ever before, but the basic principles of operation remain the same. Truck diesels are growing in popularity. In 2004, the light-truck market represented about 3 million vehicles in the United States and is expected to grow to 6.8 million by 2008.