Whom ever said you can't is wrong. You can run diesel in a gasoline engine, just not for very long, and only if it is mixed with enough gasoline to ignight under a spark. read more
The compression ratio in petrol engine is in the range of 1:7 to 1:10, whereas the compression ratio in diesel engine is in the range of 1:18 to 1:21 (we can easily make out the difference from the above two figures). read more