DiesOtto

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The Mercedes-Benz DiesOtto is an experimental automobile engine that “is said to incorporate the benefits of a diesel engine, but runs on regular old unleaded.”^[1]

Its name is a portmanteau of Diesel and Otto, referring to the Diesel engine, first introduced by German engineer Rudolf Diesel, and the Otto cycle, as a reference to Nicolaus Otto (even though the invention of the gasoline engine is variously attributed to both Nicolaus Otto and Alphonse Beau de Rochas).

[edit] Engine characteristics and principles of operation

The concept engine has an inline, four-cylinder configuration and displaces 1.8 litres. Its peak power is no less than 175 kW (235 hp), making its specific output 97 kW/L (130 hp/L), and its peak torque is 400 N·m, making its specific torque 220 N·m/L. Mercedes-Benz do not specify the spin rates at which these specified maxima are reached.^[2]

The DiesOtto features the following:

HCCI (Homogeneous Charge Compression Ignition);
variable valve timing;
variable geometry turbocharging;
variable compression ratio;
direct fuel injection.

It also uses a starter-alternator to reduce fuel consumption. The starter-alternator replaces the engine's flywheel, and allows the engine to be started instantaneously so that it can simply stop when not needed, such as at traffic lights, and smoothly re-start when needed.

In low demanding conditions (low to medium engine speeds), the engine uses HCCI. In high demanding conditions, it operates like a regular gasoline engine (using spark ignition of the fuel/air mixture) and uses the full benefits of direct fuel injection, turbocharging and variable valve timing to maximize efficiency. These two modes of operations require different compression ratios, which is why the engine also features a variable compression ratio.

It is reported to consume less than 6 L/100 km (47 mpg imp/39 mpg US) in the body of an S-Class. However, it is unknown in what conditions this mileage is achieved. Nevertheless, these figures are only bested by the smallest diesel engines on sale in Europe, and in far smaller cars than the S-Class.