AFTER DEPTG & CLIMBING TO 4500', THE PLT & HIS PLT RATED PAX NOTED A FUEL ODOR & RETURNED TO THE ARPT TO LAND. BFR LNDG,THE PLT CALLED THE TOWER (TWR), BUT DIDN'T ADVISE TWR PSNL OF THE FUEL ODOR OR OF A PSBL PRBLM. AS THE ACFT WAS TURNING OFF THE RWY, FIRE & SMOKE ERUPTED IN THE ENG COMPARTMENT & SPREAD BEYOND THE FIREWALL TO THE COCKPIT. THE PLT & BOTH PAXDEPLANED. A TWR CONTROLLER SAW THE SMOKE & INITIATED FIRE/RESCUE RESPONSE, BUT DIDN'T USE PROPER TERMINOLOGY. FIRE DEPT PSNL WERE DISPATCHED APRX 1 MIN LATER. BY THE TIME THEY ARRIVED, THE ACFT WAS BADLY DAMAGED. MOST OF THE ENG'S FIRE DAMAGE WAS ON ITS LEFT SIDE. WHEN TESTED, SVRL FUEL LINES/COMPONENTS LEAKED, BUT THEY HAD FIRE DAMAGE & THE EXACT IN-FLTFUEL LEAK WAS NOT VERIFIED. FUEL STAIN/DISCOLORATION WAS NOTED WHERE THE AIR THROTTLE METERING UNIT LEAKED AT AN O-RING.THERE WAS A FUEL LEAK AT THE IDLE FUEL ADJUSTMENT SCREW, ALTHO IT WAS 'FROZEN' IN A FIXED PSN. ALSO, BEECH HAD RCMDD REPLACING THE FUEL LINES EVERY 5 YRS, BUT NO RECORD WAS FND OF THEIR REPLACEMENT DURING THE LAST 5 YRS.