Antimatter reactions are quite awkward things to make use of on a small scale, or in the presense of delicate things like people or electronics.
About a third of the energy liberated by the reaction comes out in the form of gamma rays. These won't be absorbed well by the fuel you're burning, but will heat up the engine block pretty effectively.
Most of the rest of the two thirds of the energy released comes out in the form of charged pions. Some of these will do interesting things to your fuel and heat it up (which is good!) but more are likely to just heat up your engine block (which is quite bad) and depending on how much shielding you have plenty more will just sail out into the space around your engine and decay into gamma rays out there. You'll need a decent amount of radiation shielding, and a decent amount of cooling. This is all heavy and inconvenient.
Can I make an alternative suggestion?
I give you... the antimatter train.
The engine is basically a solid core antimatter rocket. A cylinder of some dense, high-melting point metal filled with holes for water to run through. You liberate your antimatter in the centre of the cylinder, and most of the energy of the reaction products will go to heating up the cylinder which will also do a reasonable job of shielding spectators from deadly radiation.
The antimatter rocket needs to operate at a couple of thousand kelvin to be worthwhile, but the train can get away with merely enough to generate superheated steam. Then you just use that to run a conventional piston engine, or if you're being boring, a steam turbine. Now all you need is a very small fuel tank and a generous supply of water and you're good to go.
(some inspiration from the nuclear fission trains in Singularity Sky)