Experimental Research On The Improvement Of Combustion About Homogeneous Charge Compression Ignition (HCCI) Engine Using Fuel Additives

The advantages of HCCI are numerous comparing with the traditional engine. Relative to SI gasoline engines, HCCI engines are more efficient, because they have no elimination of throttling losses, use the high compression ratios and have shorter combustion duration. Relative to CIDI engines, HCCI engines have extraordinarily lower emissions of PM and NOx and can offer more power as high as CIDI engines with the dilute homogeneous air and fuel mixture. Nevertheless, HCCI also has its drawbacks. It is prone to misfire at the low engine load and knock at the high load. The operating range of HCCI is narrow. HC and CO emissions are very high.To control the ignition timing and extend the operating range of HCCI, the experimental research of HCCI combustion process was carried out on a 4-cylinder diesel engine. One of the cylinders was modified for HCCI combustion with additives. The influence of additives on the HCCI engine ignition and combustion process was investigated.The experimental results indicated that under the steady operating conditions, the ignition timing of the base fuel (PRF90-90% iso-octane+10% n- heptane), which is equivalent to RON 90, delayed and the peak value of the heat release rate was low compared to the base fuel with single additive (Ditert-butyl peroxide-DTBP, Dicumyl peroxide-DCP, Tert-butyl hydroperoxide-TBHP, Tert-butyl cumyl peroxide -TBCP or Cumene hydroperoxide-CPO) which advanced ignition timing and increased the peak of the heat release rate obviously. At the conditions with the same fuel injection quantity per cycle and the same engine speed, with the increase of the additive mass fraction in the fuel, the ignition and heat release timings brought forward, the peak of heat release rate increased and the operating range at low engine load was enlarged obviously. However, excessive additives will make the engine be prone to knock, run rudely and shorten the operating range at high engine load. Finally, the DTBP additive is the best one with the best mass concentration 2%.For improving the combustion of HCCI, we need the answer is that: whether the single additive is the best choice? The experimental results indicated that the mixed additives (M1- DTBP+TBPB, M2-DTBP+DTAP, M3-DTBP+TBPB+DTAP +TBHP) were better than the single additives for HCCI fuel, since the ignition and heat release timings advanced and the peak of heat release rate increased at different engine speeds and steady the operating conditions. Moreover, with the increase of engine speed, the influence of mixed additives on HCCI combustion was more obvious. In addition, the mixed additives were beneficial to improve HCCI engine misfire at the high engine speed. Comparing with other mixed additives, M1 is the best one to be chosen.All in all, additives are beneficial to improve the ignition of HCCI at low engine load and extend the operating range. Nevertheless, the knock happens obviously while the range is extending at the high engine speed and load. For solving the paradox, the antiknock and EGR can be used.