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A system for injection of diesel fuel and water with real-time control, or real-time water injection (RTWI), was developed and applied to a heavy-duty diesel engine. The RTWI system featured electronic unit pumps that delivered metered volumes of water to electronic unit injectors (EUI) modified to incorporate the water addition passages. The water and diesel mixed in the injector tip such that the initial portion of the injection contained mostly diesel fuel, while the balance of the injection was a water and diesel mixture. With this hardware, real-time cycle-by-cycle control of water mass was used to mitigate soot formation during diesel combustion. Using RTWI alone, NOx emissions were reduced by 42%. Using high-pressure-loop exhaust gas recirculation (EGR) and conventional diesel combustion with RTWI, the NOx was reduced by 82%.

Despite being developed more than 100 years ago, the diesel engine has yet to achieve mass acceptance in the North American passenger car sector. In most other parts of the world, however, diesel engines have made considerable strides due in part to the common rail fuel injection system. Significant fuel economy, reduced exhaust emissions, invincible low-speed torque, and all-around good drivability are a few of the benefits associated with common rail technology, which are covered in-depth in Diesel Common Rail and Advanced Fuel Injection Systems.