Volumetric fluid expander with water injection

A method for recovering exhaust gas energy, the method comprising:

• injecting, by a water injection mechanism, water into a cylinder of an engine at or before an exhaust cycle of the cylinder, wherein the injected water vaporizes within the cylinder;
• collecting, via an exhaust manifold of the engine, exhaust gas stream mixed with the vaporized water;
• supplying the exhaust gas stream into a volumetric fluid expander, the exhaust gas stream having a first pressure;
• and
• generating, by the volumetric fluid expander, useful work at an output shaft of the expander by expanding the exhaust gas stream to a second pressure lower than the first pressure.

An exhaust gas energy recovery system comprising:

• a. an internal combustion engine having a cylinder and an exhaust gas outlet for conveying an exhaust gas stream at a first pressure;
• b. a volumetric fluid expander including:
• i. a housing having an inlet and an outlet, the housing inlet being in fluid communication with the exhaust gas outlet;
• ii. an output shaft;
• iii. wherein the volumetric fluid expander is configured to generate useful work at the output shaft by expanding the exhaust gas stream to a second pressure lower than the first pressure generally without reducing the volume of the exhaust stream as the exhaust stream moves from the housing inlet to the outlet;
• and
• c. a water injection mechanism configured to inject water into the cylinder such that the exhaust gas stream received by the volumetric fluid expander is increased in volume.