Ammonium nitrate does not require fuel to detonate. Even if you add heavy diesel, you will still be need to use the same boosters (usually PETN) that you would use for pure ammonium nitrate to achieve reliable detonation. Ammonium nitrate has a positive stoichiometric oxygen balance when it detonates so it is typically mixed with chemicals with a negative oxygen balance (such as heavy diesel) to inexpensively improve explosive performance. It has nothing to do with making it detonate.

While ammonium nitrate is quite difficult to detonate at room temperature, it becomes considerably less stable as it approaches its melting point, which is relatively low. Sensitivity can also be increased chemically but that requires significant effort and intent.