A Fundamental Study on CH* and OH* Flame Emissions as Indicators of Heat Release and AFR at Engine Relevant Conditions of Temperature and Pressure

英国95%以上的能源需求都是燃烧，因此先进的燃烧监测和测量技术对于开发清洁高效的发动机、锅炉和熔炉至关重要。火焰化学发光是由燃烧过程中形成的中间（自由基）化学物质发出的光，长期以来一直被认为可以提供有关反应区中发生的化学过程的详细信息，例如局部空燃比和燃料消耗率。然而，在已发表的文献中，关于将化学发光测量结果解释为局部热释放率和空燃比的指标-这些参数对发动机和燃烧器的燃烧研究人员具有极大的兴趣和重要性-存在相互矛盾的信息。因此，这项工作的总体目标是确定是否从两个自由基物种，通常发生在碳氢化合物火焰中的化学发光强度（OH* 和CH*）可用作在“发动机相关”条件下的放热速率的量度，以及它们的相对强度是否可以用来确定空燃比。基本的燃烧实验将在一个球形容器中进行，中央点火和窗户-也被称为燃烧弹。将制备空气、燃料和残余燃烧气体的均匀混合物（代表内燃机中通常遇到的条件范围）并在容器中燃烧。由此产生的OH* 和CH* 光发射将由装有适当光谱滤波器的光电倍增管记录。燃烧弹方法在许多方面都非常有利于这项工作：点火后，球形火焰通过混合物径向传播，在火焰前缘之前压缩未燃烧气体。因此，火焰化学发光数据是从一个单一的实验中获得的一系列的温度和压力。燃烧弹允许在广泛的压力和温度范围内收集数据（可以研究高达30 bar的压力和高达850 K的未燃烧气体温度）。此外，通过改变初始温度和压力，可以解耦压力和温度的影响，并生成温度和压力对OH* 和CH* 化学发光强度的影响的相关性。牛津大学的内燃机小组（ICEG）在燃烧弹实验方面有着丰富的经验（超过16年）。从这些以前的工作中获得的经验导致了该领域的3个显着创新：+使用自由落体实验来消除浮力的影响。采用多区燃烧模型进行数据分析，从而将燃烧气体中的离解效应和温度梯度（通常为500 K）纳入火焰前沿位置和压力上升的分析中。+与使用固定组成的N2/CO2混合物来表示残余物的常规方法相反，通过保留先前燃烧事件的一部分作为残余物来使用“真实的残余物”。（但不简单）可以精确控制和分析的燃烧实验-与发动机不同，未燃烧气体的温度可以精确计算，在实验结束之前，没有移动活塞，也没有热量传递到外壳。2这项工作不需要购买主要的硬件。现有的燃烧弹设施，它使用一个全面的LabVIEW接口设置实验条件和数据记录，是可用的，因为是光电倍增管和经过验证的多区燃烧模型和以前开发的MATLAB程序的数据分析。

Over 95% of the UK energy needs utilize combustion, so advanced combustion monitoring and measurement techniques are essential to the development of clean and efficient engines, boilers and furnaces. Flame chemiluminescence, which is light emitted from intermediate (radical) chemical species formed during combustion, has long been thought to hold detailed information about the chemical processes occurring in the reaction zone, such as the local air-fuel ratio and fuel consumption rate. However, there is conflicting information within the published literature as to the interpretation of chemiluminescence measurements as indicators of local heat release rate and air fuel ratio - parameters that are of tremendous interest and importance to combustion researchers of engines and burners. Accordingly, the overall objective of this work is to determine whether the chemiluminescence intensity emitted from two radical species that commonly occur in hydrocarbon flames (OH* and CH*) can be used as a measure of heat release rate under 'engine relevant' conditions, and also whether their relative intensities can be used to determine the air fuel ratio.Fundamental combustion experiments will be performed in a spherical vessel with central ignition and windows - otherwise known as a combustion bomb. Homogeneous mixtures of air, fuel, and residual combustion gases (representative of the range of conditions typically encountered in combustion engines) will be prepared and burnt in the vessel. The resultant OH* and CH* light emissions will be recorded by photomultiplier tubes fitted with appropriate spectral filters. The combustion bomb method is highly advantageous for this work in many respects: after ignition, a spherical flame propagates radially through the mixture compressing the unburned gas ahead of the flame front. Thus, flame chemiluminescence data is obtained for a sequence of linked temperatures and pressures from a single experiment. The combustion bomb allows data collection across a wide range of pressure and temperature (pressures up to 30 bar and unburned gas temperatures up to 850 K can be investigated). Moreover, by varying the initial temperature and pressure, the effects of pressure and temperature can be decoupled and correlations generated for the effect of temperature and pressure on the OH* and CH* chemiluminescence intensity. The Internal Combustion Engines Group (ICEG) at Oxford University has substantial experience (over 16 years) with combustion bomb experiments. The experience gained from these previous works has led to 3 notable innovations in the field:+ The use of free-fall experiments to eliminate the effect of buoyancy.+ The introduction of a multi-zone combustion model for data analysis, so that the effect of dissociation and the temperature gradient in the burned gas (typically 500 K) is incorporated into the analysis of flame front position and pressure rise.+ The use of 'real residuals' by retaining part of the previous combustion event as residuals, as opposed to the conventional approach of using a fixed composition N2/CO2 mixture to represent the residuals.Compared to engines, the combustion bomb provides a simplified (but not simple) experiment with combustion that can be accurately controlled and analysed - unlike an engine the temperature of the unburned gas can be calculated accurately, there is no moving piston, and no heat transfer to the enclosure before the end of the experiment.No major hardware purchases are required for the work. The existing combustion bomb facility, which uses a comprehensive LabVIEW interface for setting-up the experimental conditions and data logging, is available, as are photomultiplier tubes and a well-validated multi-zone combustion model and previously developed MATLAB routines for data analysis.