Year after year, as emission regulations become more and more stringent, internal combustion engines are going through a nearly continuous improvement process and research of new technologies to reduce specific consumption, strictly related to CO2 emissions, is an inevitable step. Nowadays, the main solution applied to gasoline engines is Gasoline Direct Injection (GDI) combined with turbocharging, which allow to increase engine efficiency, thus reducing fuel consumption. However, such solution suffers from knock occurrence and, in addition to that, mixture enrichment strategy for turbine protection must be included. It is estimated that lambda = 1 operation over the whole engine operating range will be required from EURO 7 (beyond 2022), so component protection strategies will no more be allowed. Water Injection inside combustion chamber seems to be an effective solution for reducing knock risk and protect components, thanks to water cooling effect.
Aim of this work is implementation and testing of a GDI demo-vehicle equipped with a water injection system. Vehicle performances and emissions have been measured performing WLTP and RDE homologation cycles, the former on roller bench, the latter on road. Looking at EURO 7 regulation, lambda = 1 calibration on whole engine map has been implemented to perform homologation cycles. Pollutant emissions and fuel consumption have been measured and compared to the ones measured with vehicle running in its baseline configuration.
No appreciable advantages due to water injection have been observed on WLTP cycles, since engine operating points explored during such cycle lie in low and medium speed/load areas. Conversely, RDE cycles explore high load engine map areas, where water injection is actuated consistently. Such engine regions are the one where mixture enrichment for component protection is largely present. Water injection allowed lambda 1 calibration with an acceptable power reduction: thanks to that, consistent CO reduction has been experienced, since catalyst efficiency is preserved. So, water injection promises to be a key technology to enable lambda 1 calibration, supposed to be one of the main requirements of EURO 7 regulation, with the advantage of keeping the actual turbocharger technology, since component protection is guaranteed without affecting pollutant emissions.