Strategies were investigated for increased in-cylinder formation of hydrogen. The use of low intake oxygen with a post injection was proposed. An intake oxygen sweep was conducted on a lean-burn compression ignition engine by adjusting of the exhaust gas recirculation rate. The results revealed that the yield of hydrogen increased exponentially when the intake oxygen was reduced to achieve low temperature combustion. Further tests showed that low temperature combustion operation consistently produced more hydrogen than high temperature combustion for similar air-to-fuel ratios. To increase the hydrogen yield further, a post injection timing sweep was carried out with low temperature combustion operation. Increased yields of hydrogen were obtained, up to 0.76% by volume, when then the post injection timing was advanced from 70 to 20 degrees crank angle after top dead centre. At the same time, the indicated NOx emissions reduced to 0.013 g/kW.hr and the smoke emissions were 0.14 FSN. Thus, the tests established that the combination of low temperature combustion, low intake oxygen, and an early post injection produced a high yield of hydrogen with simultaneously ultra-low NOx and smoke emissions. The main drawback of this strategy was the increased formation of methane, up to 3015 ppm by volume. However, further analysis showed that the hydrogen to methane ratio actually increased under low temperature combustion operation. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.