Tham khảo tài liệu 'internal combustion engines fundamentals episode 2 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 690 INTERNAL COMBUSTION ENGINE FUNDAMENTALS FIGURE 12-10 Surface temperature measured with thermocouple in cylinder head and surface heat flux calculated from surface temperature as a function of crank angle. Spark-ignition engine operated at The heat flux components at each frequency that caused that variation can be calculated via Fourier s law Eq. and summed to give the total fluctuation of heat flux with time k .J 7 Tm - 7Ị k 0n AB B cos ncot - A - Bn sin ncot 1 1 Alternative approaches for solving Eq. are through use of an electrical analogy to heat flow and by numerical methods. The latter become necessary if wall material properties depend significantly on temperature as do combustion chamber deposits and some insulating ceramic materials. Several measurements of this type in spark-ignition and diesel engines have been made. A summary of these measurements can be found in Ref. 9. Radiant heat fluxes are determined by a variety of techniques . photodetector and infrared monochromator thermocouple shielded by a sapphire window pyroelectric thermal detector. Spark-Ignition Engine Measurements Figure 12-10 shows the surface temperature variation with crank angle and the heat flux variation calculated from it on the cylinder head of a spark-ignition engine at a part-load low-speed operating condition. The swing in surface temperature at this point about halfway from the on-the-cylinder-axis spark plug to the cylinder wall is 7 K. The heat flux rises rapidly when the flame arrives at the measurement location has its maximum at about the time of peak cylinder pressure when gas temperatures peak see Section and then decays to relatively low levels by 60 ATC as expansion cools the burned gases. Peak heat fluxes on the cylinder head of to 3 MW m2 were measured over the normal engine speed and load 35 The heat flux profile varies significantly with location and from one cycle to the next. Figure 12-11 .
