A two-stroke engine, especially for a portable handheld work apparatus, includes a combustion chamber configured in a cylinder. The compositions of the invention are useful in the preparation of polyurethane and polyisocyanurate foams. Because the input path is continuous, efficiency is increased and impact on the user’s body is reduced thereby reducing discomfort and physical demands on the user’s body. Software configuration information may then be automatically provided to a user based at least in part on a relationship between the first and second containers at a given point in time.