In the current study, the effects of diisopropyl ether were experimentally investigated on combustion, performance, emissions and operating range in a homogeneous charged compression ignition (HCCI) engine. For this purpose, a single cylinder, four stroke, port injection test engine was run with different lambda values between 1.69 and 3.08 on HCCI mode with pure n-heptane, 20% diisopropyl ether 80% n-heptane (D20N80), and 40% diisopropyl ether 60% n-heptane (D40N60) fuel blends at full load. HCCI engine was operated between 800 and 1600 rpm engine speed at constant inlet air temperature of 60 degrees C and wide open throttle (WOT). The effects of diisopropyl ether addition were observed on cylinder pressure, heat release rate (HRR), combustion duration (CD), indicated mean effective pressure (imep), brake torque, power output, specific fuel consumption (SFC) and exhaust emissions. Test results showed that the increase of lambda leads to lower in-cylinder pressure and HRR. The addition of diisopropyl ether caused to retard combustion. Indicated thermal efficiency (ITE) increased 4.92% with D40N60 compared that n-heptane at 1200 rpm and lambda = 2. Brake torque and power output increased by about 1.03% and 1.18% with D20N80 according to pure n-heptane at 1200 rpm respectively. On the contrary, SFC decreased 24.08% with D40N60 compared to n-heptane at 1200 rpm and lambda = 2. HC and CO increased with the addition of diisopropyl ether. The test results also showed that the addition of diisopropyl ether expanded the HCCI combustion towards to knocking and partial combustion zone.