An optical engine includes a light source, an optical main body and a
projection lens. The optical main body includes a reflective light valve,
a case, a first heat-dissipating device and a heat-insulating device. The
reflective light valve reflects the incident light beam to form an image
light beam or a dumped light beam that is not projected into the
projection lens. The case encloses the light paths of the incident light
beam, the image light beam and the dumped light beam. An opening is on
the case for the dumped light beam to be projected into. A first
heat-dissipating device is fixed on the case and covers the opening for
removing the heat generated by the dumped light beam. A heat-insulating
device is disposed between the first heat-dissipating device and the case
for preventing the heat conduction between the first heat-dissipating
device and the case.