Comprehensive analysis of the possibility of the improvement of combustion and reduction of NO and CO emissions for HCCI engine operating on syngas air mixture through the production in the intake charge highly reactive species, such as singlet delta oxygen O-2(a(1)Delta(g)) or ozone molecules, is conducted. The computations with the usage of detailed reaction mechanism of syngas oxidation, involving the reactions with O-2(a(1)Delta(g)) and O-3 molecules, have showed that the abundance of O-2(a(1)Delta(g)) or O-3 molecules in the charge accelerated the ignition and made it possible to increase slightly the mass specific energy released during HCCI combustion and to reduce simultaneously the NO and CO emissions both at nominal and at low load regimes. Moreover, the production of O-2(a(1)Delta(g)) or O-3 molecules in the charge even in a small amount allows one to extend the range of stable combustion toward the extremely fuel lean mixture and ensure the stable operation of HCCI engine at low load. The advance in the energy released during combustion due to the presence of O-2(a(1)Delta(g)) or O-3 in the charge is substantially greater the energy needed for the production of O-2(a(1)Delta(g)) and O-3 molecules. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.