An internal combustion engine assembly comprising a fuel reformer, a combustion chamber and a controller. The fuel reformer comprises a first channel and a second channel, a portion of the second channel being adjacent to a portion of the first channel to facilitate heat exchange between the first and second channels. The first channel comprises a catalyst selected to reform ammonia to hydrogen and nitrogen. The first channel is configured to receive ammonia, pass the ammonia over the catalyst and output a first mixture comprising ammonia, hydrogen and nitrogen. The composition of the first mixture depends on a first reformer temperature of the first channel. The combustion chamber is configured to receive the first mixture from the fuel reformer; to receive an oxidant; to combust the first mixture in the oxidant to produce heat and a first product; and to output the first product. The second channel of the fuel reformer is configured to receive the first product.