摘要
燃燒過程是研究柴油機缸內(nèi)工作過程的關(guān)鍵，而燃燒過程與傳熱是相互耦合的，其中的傳熱主要為熱對流和熱輻射。柴油機缸內(nèi)熱對流的研究已有較為成熟的理論和經(jīng)驗公式，可以較合理地預(yù)測對流換熱量的大小。而對柴油機缸內(nèi)的熱輻射的研究，由于輻射傳熱的復(fù)雜性，目前一般資料還沒有詳細的介紹，但是實驗研究的結(jié)果表明，對于大中型柴油機，其缸內(nèi)輻射傳熱量占總傳熱量的10％～45％。隨著計算機技術(shù)和測試技術(shù)的發(fā)展，使柴油機缸內(nèi)熱輻射問題的深入研究成為可能。本文對可用于缸內(nèi)輻射換熱計算的各種模型進行比較，以尋找能夠準(zhǔn)確合理地模擬柴油機缸內(nèi)輻射傳熱情況的模型方法。
本文的研究對象為G4135直噴式柴油機，首先用前處理軟件GAMBIT建立燃燒室模型，燃燒室的網(wǎng)格采用分塊網(wǎng)絡(luò)劃分法，劃分網(wǎng)格后導(dǎo)入FLUENT軟件生成動網(wǎng)格，然后分別用離散傳遞模型（DTRM）、Rosseland輻射模型、離散坐標(biāo)輻射模型（DO）以及P-1近似輻射模型對柴油機缸內(nèi)的輻射物性參量進行模擬。
首先對輻射吸收系數(shù)、輻射熱流密度進行模擬，結(jié)果表明其隨曲軸轉(zhuǎn)角的變化規(guī)律符合燃燒的一般規(guī)律；隨后對碳煙濃度進行模擬，結(jié)果表明DO模型模擬出的碳煙濃度與實驗數(shù)據(jù)吻合最好，P-1模型次之，其它輻射模型的模擬結(jié)果與實驗值差距很大；接著分別用DO模型和P-1模型對燃燒室內(nèi)的輻射溫度和平均氣體溫度進行模擬，計算出該情況下的火焰溫度，將計算得到的火焰溫度與實驗測得的火焰溫度進行比較，結(jié)果表明DO模型模擬出的結(jié)果與實驗值兩者差距僅8％，而P-1模型與實驗值相差31％，驗證了DO模型在模擬柴油機缸內(nèi)的輻射傳熱過程方面具有一定的可靠性。隨后運用模擬效果較好的DO模型，對構(gòu)成柴油機燃燒室的不同零部件的輻射傳熱情況進行模擬分析，并研究了不同轉(zhuǎn)速和負荷對輻射溫度、碳煙濃度和輻射熱流密度的影響，結(jié)果表明輻射溫度、碳煙濃度和輻射熱流密度隨著負荷的增加而增大，隨著轉(zhuǎn)速的下降而上升，且輻射傳熱量占總傳熱量的份額為26％～48％。
本文的研究方法和結(jié)果可以對同類型柴油機的輻射傳熱研究起到拋磚引玉的作用。

關(guān)鍵詞 輻射傳熱；柴油機；輻射模型；FLUENT；燃燒













Abstract
To study the working process of the diesel engine, the combustion process is the key, and the combustion process is coupled with the heat transfer. The main heat transfer of combustion process is convection heat transfer and thermal radiation. The study on convection heat transfer in cylinder has got mature theory and empirical formula, so the size of convective heat transfer can be predicted reasonably. Due to its complexity of the study of thermal radiation, general information has not described in details yet, but experiment studies have concluded that, for large diesel engines, the radiation heat transfer medium of its total radiation heat transfer from 10% to 45%. With the development of computer technology and testing technology, the depth study of heat radiation in diesel engine cylinder turns possible. This article is intended to find a radiation model which can accurately simulate the radiation heat transfer in cylinder.
In this paper, the G4135 diesel engine model was taken as an example. First, GAMBIT was used to build the model of the combustion chamber, and grid of combustion chamber is divided by block network, then import into FLUENT software after meshing. And then use the model such as Discrete transfer radiation model (DTRM), Rosseland radiation model, discrete ordinates radiation model (DO) and the P-1 radiation model provided by FLUENT software, to analyze the physical parameters of radiation in cylinder.
First, the radiation absorption coefficient and radiation heat flux was simulated, and the results showed that their variation with crank angle agreed with the general rules of combustion; Then the soot density was simulate, the results showed that the soot density simulated by DO radiation model in the best agreement with experimental data, followed by P-1 radiation model, but simulation results of the other radiation models was different from experimental data greatly; Then DO radiation model and P-1 radiation model were used to simulate radiation temperature and the average gas temperature in combustion chamber, and calculate the flame temperature under these conditions, compared the calculated flame temperature with the experimental flame temperature, the results simulated by the DO radiation model differ from the experimental data with t only 8%, while the P-1 radiation model with 31%, which verified that the DO radiation model has some reliability in simulating the radiation heat transfer in diesel engine cylinder. Then use the DO radiation model which was a better simulation model, to simulate and analyze the radiation heat transfer of different parts of the combustion chamber, and study the different speed and load how to impact the radiation temperature, soot density and the radiation heat flux, the results show that the radiation temperature, soot density and radiation heat flux is proportional with the load, and inversely with the speed, and radiation heat transfer shared from 26% to 48% of total heat transfer.
This study method and results can give better ideas to be the study of the radiation heat transfer of the same type of engine.

Keywords radiation heat transfer；Diesel engine；radi..