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A naturally aspirated, four-cylinder diesel engine was retrofitted with multipoint liquefied petroleum gas (LPG) port injection while retaining mechanical direct injection of B7 diesel. Twenty operating points at 1400 and 2400 rpm covered LPG energy fractions of 13.45–38.25%. Fuel balances, cylinder pressure, apparent heat release, gaseous emissions, filter smoke number (FSN) and particle number concentration (PN) were evaluated concurrently. At 1400 rpm, intermediate-load operation with 31.37–38.25% LPG energy fraction improved brake thermal efficiency (BTE) and lowered FSN and PN together, while the lowest load exhibited an efficiency penalty. At low load and 2400 rpm, higher BTE was accompanied by delayed heat release and incomplete oxidation. Carbon monoxide and total hydrocarbon emissions increased at all dual-fuel operating points relative to baseline B7 operation. At the highest loads, lower FSN coincided with PN increases of 55.85–179.78% at 1400 rpm and 149.03% at 2400 rpm. Rapid pressure development and combustion oscillations restricted high-load enrichment to 24.40% at 1400 rpm. Under these conditions, an analysis of 200 cycles yielded coefficients of variation of 1.57% for gross indicated work and 15.02% for maximum pressure-rise rate (MPRR). The MPRR calculated from the mean pressure trace was 11.43% lower than the mean of the MPRR values calculated for individual cycles. LPG enrichment therefore involved competing efficiency, oxidation, particle-number and pressure-rise responses that varied with speed and load.