Reactivity controlled compression ignition (RCCI) is demonstrated as a controllable high efficiency and clean combustion strategy, which is confirmed to be affected by either inlet pressure (IP), total cycle energy (E-total), or start of injection (SOI). This paper discussed their combined effect on low load RCCI combustion and emission characteristics in a multi-cylinder heavy-duty engine fueled with gasoline/diesel. Results show that low temperature heat release (LTHR) only occurs when SOI is sufficiently advanced. Combustion duration (CD) is lengthened, shortened and unchanged with SOI advance under different E(total)s, while lengthened with IP increase. NOX emission first increases and then decreases with SOI advance, and declines with IP increase or E-total decrease. Trend CO changes with SOI or IP becomes opposite at the lowest E-total, comparing with that at relatively high E(total)s. HC emission decreases with SOI advance or E-total increase, while it is insensitive to IP. Trend number of nuclear particle (Num(n)) changes with IP becomes opposite at the highest E-total, comparing with that at relatively low E(total)s, while Num(n) decreases with SOI advance or E-total increase. Both number of aggregated particle (Num(a)) and soot first decreases and then increases with SOI advance, and decreases with E-total decrease or IP increase. (C) 2018 Elsevier Ltd. All rights reserved.