Heat transfer coefficient on the combustion chamber wall surfaces in a naturally aspirated direct-injection diesel engine

Abstract

Thin-film thermocouples were used to measure the instantaneous temperature at 100 points on all the combustion chamber wall surfaces in a naturally aspirated direct-injection diesel engine. Instantaneous heat flux at each measured point was also obtained through heat transfer analysis with the measured instantaneous wall surface temperature applied as a boundary condition. In addition, the instantaneous mass-averaged gas temperature in the combustion chamber was calculated through the equation of state of an ideal gas. As a result, the local and overall heat transfer coefficients were evaluated using the corresponding wall surface temperatures and heat fluxes. The overall heat transfer coefficients thus obtained were compared with those calculated with Eichelberg's and Woschni's empirical equations for five ignition timings and three engine speeds. As a result, it was revealed that an overall average heat transfer coefficient obtained through the authors' experiments has characteristics different from those of the heat transfer coefficients calculated from the empirical equations proposed by Eichelberg and Woschni.

High-frequency wall heat flux measurement during wall impingement of a diffusion flame

“…The convection coefficient value of h ∼10 kW/m 2 /K is two to five times higher than those obtained by previous experimental 24 or correlation-based 39 studies. Most likely that is due to differences in the experimental setup (engine instead of CV chamber cases).…”

“…In CI engines, the combustion phenomena are different (spray mixing, diffusion flame). 23 Heat flux measurements therefore yield different features, 8,9,24 with heat fluxes as high as 10 MW/m 2 exhibiting a plateau of a few milliseconds rather than a spike of heat flux. 25,26 Extensive studies 27–29 about diesel jet impingement showed that a cool flame develops close to the wall, due to either higher premixing or because of extinction of the diffusion flame or dying flame, although it is still surrounded by high temperature reactions at the diverted tip, in some cases leading to the deposition of soot.…”

Effect of combustion regime on in-cylinder heat transfer in internal combustion engines

“…As discussed in section ‘Comparison of in-cylinder pressure and heat release rate for the three combustion regimes’, the heat flux in the CDC combustion process strongly depends on the flame evolution and in-cylinder turbulence, which are not considered in the empirical heat transfer correlations. Moreover, Enomoto et al 56 found that the Woschni model cannot accurately reproduce the heat transfer losses of a light-duty diesel engine under various engine speeds. Thus, by reviewing empirical heat transfer correlations available in the literature, Finol and Robinson 57 concluded that these empirical models should be improved by taking account of the non-uniform in-cylinder flow and thermal fields, particularly in the boundary layer.…”

Investigation of heat transfer in combustion chamber of a direct injection diesel engine under different compression ratios and engine torques

“…Çalışmada, motor sıkıştırma oranı ve devir değişiminin yanma odası ısı geçişine büyük oranda etki ettiği belirlenmiştir. Başka bir çalışmada [7] tek silindirli hava soğutmalı sıkıştırma ateşlemeli bir motorda yanma odasında çeşitli noktalarda duvar yüzey sıcaklığı ve ısı kayıpları deneysel olarak incelenmiştir. Çalışmada, Woschni ve Eichelberg ısı taşınım katsayısı denklemlerini kullanarak elde edilen ısı geçişi deneysel sonuçlarla kıyaslanmış ve Woschni denkleminin daha yüksek, Eichelberg denkleminin daha düşük değerler verdiği gösterilmiştir.…”