Everyone has been behind a bus or a truck and been "smoked" by the diesel exhaust; which has, unfortunately, shaped our perceptions of what diesels are like. Modern Mercedes diesels are NOTHING like truck or bus engines, save the underlying principle by which they operate. Let's lift the veil and increase our understanding of the diesel engine, since, after all, Mercedes-Benz (I can't seem to get the hang of saying Daimler Chrysler yet) produced the world's first production diesel-engined passenger car in 1936 (260D), and they still lead the world today. Diesel engines have been around as long as the gas "Otto-Cycle" engines, yet myths and misconceptions abound. Diesel engines are similar to their gas brethren in that they have cylinders, pistons, crankshafts, and valves, but they differ in one key area: Ignition. Gas engines ignite a mixture of gasoline and air using a spark of electricity but diesels use heat. If air is compressed sufficiently, which Rudolf Diesel realized, it will heat up to the point that injected fuel will begin burning spontaneously. In a diesel engine, pistons squeeze air to up to 23 times normal atmospheric pressure, which heats the air to a degree that injected fuel immediately burns, producing an explosive force to eventually propel the car. Simple and elegant!
What's so great about diesels you might ask? They are significantly more efficient engines, thus they can get more miles per gallon of fuel and can travel further on a tankful. Since diesels must withstand greater forces than their gasoline counterparts, they are robustly designed and can last up to twice as long on the average before major engine work is required, provided that engine fluids and filters are changed religiously. Finally, no tune-ups are required on diesels, since there are no ignition components such as spark plugs and wires, distributors, coils, or rotors to replace.
Despite common beliefs to the contrary, properly maintained Mercedes diesels can be started in below-zero weather. Buying good quality diesel fuel, using a premium battery, maintaining high engine compression, and ensuring properly functioning glow-plugs are the keys to starting success in the dead of winter. In a process called "pre-glowing", diesels have glow plugs that must warm up before the engine is started, which takes a moment or two. Unfortunately, most folks are spoiled by immediately starting gas engines and thus reject diesels for that reason. I once heard that the time required to heat the glow plugs could be viewed as "A pause in honor of Rudolf Diesel". Well said. Once diesels are fully warmed up though, no pre-glowing is required. Most Mercedes diesels are turbocharged today, which significantly boosts power, but that's a whole new topic of discussion for later.
Diesel aficionados often speak of their engines with a fervor and passion that escapes us gas engine owners. What is it about diesels that can inspire such loyalty and devotion? I'm envious. Perhaps "dieselheads" enjoy being a little different, or perhaps they know the secret that in the long run they can drive to the end of the road and BACK.
Steven Rae, Technical Advisor