Experimental and Numerical Study of the Water Injection to Improve the Fuel Economy of a Small Size Turbocharged SI Engine

Paper #:
  • 2017-01-0540

Published:
  • 2017-03-28
Abstract:
In this work, a promising technique to overcome overfueling and delayed combustions typical of downsized turbocharged engines is investigated, consisting in a liquid Water Injection (WI) at the intake ports. In a first stage, the engine is experimentally characterized at a fixed speed, medium-high loads, and variable spark timings, ranging from knock-safe operations up to knocking ones. For each tested point, a water-to-fuel ratio sweep is realized, aiming to prove the water capability in increasing the engine knock resistance. In a second stage, the engine is schematized in a 1D framework. The 1D model, developed in the GT-Power™ environment, makes use of user defined sub-models for the description of combustion and knock phenomena. The latter models are validated against the experimental data for all the considered operating points, both in terms of average performance parameters, in-cylinder pressure cycles and burn rate profiles. Finally, the validated model is used to carry out a numerical engine calibration in presence of water injection at the speed of 3500 rpm and at medium-high load levels, aiming to maximize the fuel economy. The presented results highlight that the investigated technique involves significant Brake Specific Fuel Consumption (BSFC) improvements, especially at the higher loads. However, the above advantages are limited by the maximum allowable in-cylinder pressure, turbine inlet temperature, turbocharger speed, and boost level. Both experimental and numerical results prove the effectiveness of the WI as a path to improve the fuel economy at high loads. The developed numerical procedure, taking into account the complex interactions among different driving parameters affecting the engine behavior, showed the potential to realize a numerical engine pre-calibration and to realistically predict the WI-related BSFC advantages.
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