This program used a 0.6 liter DI NA single cylinder diesel engine to study the influence of ferrocene as a fuel additive on particulate and NOx emissions and heat release rates. Previous Studies1,15 have shown efficiency and particulate emission benefits only after engine conditioning. Two engine configurations were tested: standard aluminum piston with normal engine deposits and a second test with the engine cleaned to “new engine condition”, but with the piston replaced with a thermal barrier coated piston. Particle concentration and size in roughly the 7.5 to 750 nm diameter range were measured with a condensation nucleus counter and an electrical aerosol analyzer. Heat release rates and IMEPs were calculated from in-cylinder pressure data. Particle number concentrations increased substantially when the 250 ppm dose was first started with both engine configuration, but decreased 30% to 50% with conditioning. Nanoparticle concentrations (diameter < 50 nm) appear to be sensitive to small changes in heat release rates, so these particulate trends suggest surface conditioning that produces changes in heat release patterns. Heat release profiles showed an intriguing shift during one 175 minute period of stable aluminum piston operation. The 30 and 40% burn angles advanced while 5 and 60% burn angles remained unchanged. This shift in heat release was associated with reductions in NOx and exhaust temperature along with a 40-50 K decrease in calculated peak in-cylinder temperature.