Optical Diagnostics On HCCI Inhomogeneity And Biofuels Low Temperature Combustion

Homogeneous charge compression ignition (HCCI) and low temperature combustion (LTC) are considered to be the most promising internal combustion engine technologies to meet more stringent emissions regulations. A couple of critical issues of HCCI and LTC were studied in this paper using conventional and optical diagnostics.First of all, to control the autoignition and extend operation range of HCCI combustion, a series of control methods including fuel properties, operating boundary conditions, mixture and temperature inhomogeneities has been studied in terms of experiments and mechanisms. Study demonstrated that more sensitive gasoline fuels had more benefits than non-sensitive fuels for applying in a HCCI engine, but appropriate control strategies were needed in order to derive the benefits of sensitive fuels. Modest inhomogeneity in fuel concentration or temperature appearing in mixing can affect the HCCI combustion process. The mixture inhomogeneity created by different port injection strategies induced the local temperature inhomogeneity, leading to different combustion process. Some of the chemical kinetic reactions are"frozen"due to the larger temperature inhomogeneities under lower coolant temperature condition. For the temperature inhomogeneities created by various squish lip configuration in the combustion chamber, different turbulence intensity was generated, which offered a potentially effective approach to modulating the HCCI combustion.However, although HCCI combustion processes can be effectively controlled, the operation range is still limited for HCCI engine. Recently, the LTC with EGR dilution has gained tremendous attention due to the fact that the control of combustion phasing is closely coupled to the fuel injection event and high-efficiency clean combustion can be achieved in full load. On the other hand, in the long run biofuel is a promising candidate due to its renewability and carbon neutrality for vehicles. Therefore, a further study aimed at LTC processes control fuelling various biofuels. Results fueling neat soybean biodiesel and neat butanol demonstrated that the butanol had a higher normalized peak pressure which excludes the effects of different energy inputs, indicating the butanol had a higher potential thermal efficiency. The flame distribution was obviously increased at 10.5% oxygen and the butanol had a lower flame luminosity compared with the soybean biodiesel. Compared with butanol, soybean biodiesel had a higher value of normalized time integrated soot mass (NTISM) and the total soot mass were sensitive to the ambient temperature for the soybean biodiesel at 10.5% oxygen. In addition, a comparative study between B20S80 (20% butanol/80% soybean biodiesel) and E20S80 (20% ethanol/80% soybean biodiesel) were carried out at different ambient temperatures (800 K?1200 K). The micro-explosion occurred for B20S80 and E20S80 at 800 K and 900 K. Compared with the B20S80, the E20S80 had higher peak pressure, lower flame luminosity, and lower value of NTISM, indicating the E20S80 fuel exhibited more advantages in combustion and emissions.Finally, it can be found that the fuel properties should be one of the important control parameters to reach high-efficiency and clean combustion in engines. More sensitive gasoline fuels have more benefits than non-sensitive fuels for applying in a HCCI engine. To the LTC in diesel engines, fuel should be with higher oxygen, higher volatility and ower cetane number. In-cylinder temperature control is another important parameter to achieve high-efficiency and clean combustion in ICEs. HCCI combustion processes can be controlled by temperature inhomogeneities and the operation range can also be extended. For the LTC in diesel engines, a lower environment temperature near the TDC should have more advantageous to the combustion and emissions control.