The use of hydrogen (H2) as a fuel for urban private and public transport may represent a major solution to reduce pollutant emissions and CO2 production in urban areas. Looking for short-term solutions, the introduction of moderate quantities of H2 (up to 30%) into Natural Gas (NG) SI engines may be a feasible solution to get a faster combustion process, and therefore less HC and CO2 emissions, and a slight NOx increase which may be potentially limited by the adoption of lean-burn engine control strategies.
However, concurrent effects of volumetric efficiency reduction and maximum temperature in the combustion chamber require a careful optimization of operating conditions to fully exploit the H2 potential and to determine the most convenient H2/NG mixture ratio.
In that context, 3D numerical tools may be useful to analyze the effect of H2 introduction on engine performance. Combustion modelling should be handled with care, since performance variation mainly depends on fuel properties (heating value, laminar flame speed) and on the effect of turbulent transport on the global turbulent flame speed.
In this paper, results concerning a project (BONGHY) to introduce H2/NG fuel mixtures into a public transport fleet are reported. Project BONGHY activities have been carried out in conjunction with ENEA, ASM and Universities of Roma La Sapienza and Cattolica di Brescia, to analyze the H2/NG mixture potential as a fuel for garbage trucks in urban areas. Results here reported particularly concern numerical activities to predict the effect of H2 introduction on final engine performance.
To that aim, KIVA-3V code has been utilized as the basic thermal-fluid-dynamic platform where an advanced combustion model (CFM) based on the flamelet assumption and suitably modified to support H2/NG mixture combustion has been implemented.
The application of the model to the analysis of several operating conditions has proved its usefulness to identify the effect of variation of engine control parameters (primarily spark advance) on performance to support experimental activities and finally get a reduction of CO2 and fuel consumption with no major penalties on tailpipe NOx emissions.