A power generation system, comprising: a diesel engine operative to produce exhaust; a fuel injector configured to inject fuel into the exhaust; a pre-combustor comprising an oxidation catalyst and configured to receive a stream of the exhaust together with fuel injected by the fuel injector; a large channel combustor comprising an oxidation catalyst in a washcoat and configured to receive the exhaust stream from the pre-combustor; a fuel reformer comprising a fuel reforming catalyst and configured to receive the exhaust stream from the large channel combustor; and a lean NOx trap configured to receive the exhaust stream from ' the fuel reformer; wherein the pre-combustor is operative to combust a first portion of the injected fuel and to vaporize another portion of the injected fuel; the system is configured to mix the exhaust and vaporized fuel between the pre-combustor and the large channel combustor; the large channel combustor has an average channel size larger than an average channel size of the fuel reformer and a thermal mass no more than about 20% that of the fuel reformer; the fuel reformer is operative to form an effective amount of H 2 and CO for denitrating the lean NO X -trap when the exhaust-fuel stream from the large channel combustor is overall rich; wherein the fuel reformer has a low thermal mass, whereby it is designed to heat to at least about 500 oC and catalyze steam reforming reaction with each denitration of the lean NOx trap; the lean NOx trap is functional to adsorb and store NO x from the exhaust stream when the exhaust stream is overall lean and to reduce and release stored NO x when the exhaust stream is overall rich; and wherein: the fuel reformer comprises an oxidation catalyst; and the large channel combustor has a higher concentration of oxidation catalyst per unit surface area than does the fuel reformer. a diesel engine operative to produce exhaust; a fuel injector configured to inject fuel into the exhaust; a pre-combustor comprising an oxidation catalyst and configured to receive a stream of the exhaust together with fuel injected by the fuel injector; a large channel combustor comprising an oxidation catalyst in a washcoat and configured to receive the exhaust stream from the pre-combustor; a fuel reformer comprising a fuel reforming catalyst and configured to receive the exhaust stream from the large channel combustor; and a lean NOx trap configured to receive the exhaust stream from ' the fuel reformer; wherein the pre-combustor is operative to combust a first portion of the injected fuel and to vaporize another portion of the injected fuel; the system is configured to mix the exhaust and vaporized fuel between the pre-combustor and the large channel combustor; the large channel combustor has an average channel size larger than an average channel size of the fuel reformer and a thermal mass no more than about 20% that of the fuel reformer; the fuel reformer is operative to form an effective amount of H 2 and CO for denitrating the lean NO X -trap when the exhaust-fuel stream from the large channel combustor is overall rich; wherein the fuel reformer has a low thermal mass, whereby it is designed to heat to at least about 500 oC and catalyze steam reforming reaction with each denitration of the lean NOx trap; the lean NOx trap is functional to adsorb and store NO x from the exhaust stream when the exhaust stream is overall lean and to reduce and release stored NO x when the exhaust stream is overall rich; and wherein: the fuel reformer comprises an oxidation catalyst; and the large channel combustor has a higher concentration of oxidation catalyst per unit surface area than does the fuel reformer. the fuel reformer comprises an oxidation catalyst; and the large channel combustor has a higher concentration of oxidation catalyst per unit surface area than does the fuel reformer.