Characteristics
Improvements in power, fuel economy and Noise, Vibration, and Harshness in both small- and large-capacity turbodiesels over the last decade have spurred their widespread adoption in certain markets, notably in Europe where they (as of 2006) make up over 50% of new car registrations. Turbodiesels are generally considered more flexible for automotive uses than naturally aspirated diesels, which have strong low-speed torque outputs but lack power at higher speeds. Turbodiesels can be designed to have a more acceptable spread of both power and torque over their speed range or, if being built for commercial use, can be designed to improve either torque or power at a given speed depending on the exact use. Naturally aspirated diesels, almost without exception, have a lower power output than a petrol engine of the same capacity whilst the same time requiring stronger (and thus heavier) internal components such as the pistons and crankshaft to withstand the greater stresses of the diesel engine's operating cycle. These factors give naturally aspirated diesels a poor power-to-weight ratio. Turbocharger units weigh very little but can offer significant power, torque and efficiency improvements—fitting a turbocharger can bring a diesel engine's power-to-weight ratio up to the same level as an equivalent petrol unit, making turbodiesels desirable for automotive use, where manufacturers aim for comparable power outputs and handling qualities across their range regardless of the type of power unit chosen.
Turbochargers are in many ways more suited to operation in diesel engines. The smaller speed range that Diesel engines work in (between 1000 and 5000 rpm for a private car, and as little as 1000-3500 rpm for a larger unit in a commercial vehicle) mean that the turbocharger has to change speed less, reducing turbo lag and improving efficiency. Diesel engines do not require dump valves (see the turbocharger article for more information). Perhaps most significantly, the diesel engine is immune from detonation because the fuel is not injected until the moment of combustion, so the compression ratio does not have to be reduced, or other anti-detonation measures taken, as would be necessary for a turbocharged spark-ignition engine.The turbodiesel engine can also help with the amount of torque it can give out. Commonly used in trucks, it helps improve the towing capacity of a truck, as well as fuel economy.
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