Structural composite manufacturing in automotive industry tends towards short cycle times for being competitive with other material solutions. Development towards resin transfer molding process can be considered when highly reactive resin with short curing cycle is used. Mixing of the resin system components is then held at the mold inlet to reduce catalyzed resin life time. Cure kinetics and viscosity changes induced during filling are thus to be taken into account when injection process simulation is considered. In the case of on-line mixing of resin components, viscosity and degree of cure of the first injected resin droplets are not the same than for the following ones. This topic will be addressed here for mixed constant flow rate and pressure injection schemes. A solution that could be implemented in a RTM simulation package was developed and validated with an analytical solution and on a complex shape automotive part demonstrator.