to burn human remains properly, the heat needs to be at 1300+ degrees 'C' for 2+ hours; then the pelvis, femurs and skulls still need a 'ball mill' to crush to a fine ash, something that isn't done here, which is why the monk with family present the following day, goes through the bones and selects some bone and ash to be placed in the urn.
Depending on the grade of Crematorium, some are oil or gas fired and cheaper Crems use wood, some even throw a few tyres on to keep the heat up.
(Excuse my frank explanation) RIP to your wife.