MAN Diesel, a renown producer of marine and power plant diesel engines, has been working on improving fuel efficiency of its engines. Today, the fuel energy efficiency is about 50%. The MAN Turbo Efficiency System (TES) allows to recover of heat from the exhaust gas, which is responsible for about 50% of the energy losses.
Here is a Sankey diagram that shows the recovery of energy from exhaust gas.
Download a description of the TES here (PDF, 291 KB) or view a high resolution version of the above Sankey diagram from their press picture gallery.