This work investigates the effects of partial HCCI (Homogeneous charge compression ignition) application on today's modern diesel engine tail pipe NOx emissions. Gasoline fumigation is supplied via a port fuel injection system located in the intake port of DI(Direct injection) diesel engine to maintain partial HCCI conditions and also diesel fuel injected directly into the combustion chamber before TDC(Top dead center). A single cylinder direct injection diesel research engine equipped with a high pressure injection system was used. Engine performance, fuel consumption, tail pipe emissions and in cylinder pressure measurements were recorded during tests. Rate of heat release and bulk temperature of medium calculated with implementing thermodynamic and gas laws to measured pressure signals. Experiments divide into two main phases which are diesel fuel tests and fumigation tests. Before the tests, maximum injectible quantity of diesel fuel was determined by considering the soot limit of the engine and fumigation ratio was 10% by volume of pre-determined diesel injection quantity. Gasoline fumigation slightly decreased engine performance at low speeds and brake specific fuel consumption increased relatively. Exhaust temperature of fumigation test was higher than that of diesel fuel tests also diffusion phase of rate of heat release curve were similar for both fuels. Depending on in cylinder pressure measurements and heat release calculations, lower heat loss from medium to the walls obtained with gasoline fumigation. Despite higher peak premixed combustion values, NOx emissions decreased significantly. On the other hand unburned hydrocarbons increased dramatically