Micro-explosion of Fuel Blends in Low Carbon Diesel Engines: Experimental and Modelling Study

运输部门占全球碳排放的很大一部分，在英国，约20%的二氧化碳排放归因于公路运输。因此，缓解二氧化碳的温室效应和减少汽车尾气排放的需要为开发更清洁、更高效的汽车动力总成和环境友好型燃料提供了动力。减少石油衍生燃料的消耗已成为21世纪的首要任务之一。由于内燃机的替代品尚未克服技术挑战，以实现在运输部门的显著利用，压燃式柴油发动机由于其高热效率，仍然是一种非常有吸引力的动力总成选择。国际能源署估计，到2050年，生物燃料占世界道路运输燃料组合的比例可能会增长到30%。这类燃料将包括生物柴油和合成柴油燃料。在同一框架内，建议将生产成本更低、二氧化碳排放量更低的非食品来源生产的生物乙醇等醇作为直接与柴油、生物柴油或合成柴油混合的替代燃料。根据我们的工业合作伙伴壳牌公司的说法，与汽油相比，巴西甘蔗生产的乙醇生产过程中产生的二氧化碳排放量低约70%。因此，乙醇-柴油混合燃料(e-柴油)作为今天和未来低碳先进柴油机的替代燃料的潜力变得非常重要。使用生物衍生燃料混合物，如电子柴油，也提供了与现有基础设施兼容的好处。另一方面，随着燃料混合物性质的复杂性增加，发动机燃烧室中出现了影响发动机性能的新现象。因此，提高科学认识对于克服潜在问题和/或获得潜在利益至关重要。一个关键现象是多组分燃料的微爆炸，在混合燃料的情况下，由于混合物中不同燃料的物理性质不同，在喷雾雾化和燃烧过程中极有可能发生微爆炸。可混溶多组分燃料液滴的微爆炸是由于不同组分之间的挥发度和沸点的差异造成的。对于不相容的多组分燃料液滴(通常称为乳化液滴)，如果低沸点组分不能溶解在混合物中并以微滴的形式在燃料液滴中扩散，则微爆炸的可能性将大大增加，例如随着生物乙醇体积分数的增加，电子柴油就是如此。柴油发动机中的微爆炸对发动机性能、燃烧和排放有潜在的重大影响。这一现象在优化喷雾燃烧系统中的装药准备方面提供了独特的潜力，使燃料雾化装置的需求和设计具有更大的灵活性。然而，尽管存在潜在的重大影响，对柴油发动机混合燃料的微爆炸仍然缺乏基本的了解。在本研究中，我们首次提出利用实验和模拟技术开展前沿性研究，以系统地研究实际柴油机条件下的微爆炸现象及其对喷雾雾化、燃烧和排放的影响。这项拟议的研究利用了极有可能发生在主动界面上的创造力，并在世界上最大的生物燃料分销商之一壳牌的支持下，在实验和模型研究人员之间的密切合作下进行了研究。研究成果将在顶级国际会议和期刊上传播。这一科学基础的发展对于英国今天和未来在清洁、高效发动机和可持续低二氧化碳燃料等先进技术方面处于世界领先地位至关重要。

The transport sector accounts for a significant part of carbon emissions worldwide and in the UK about 20% of CO2 emissions are attributed to road transportation. Consequently, the need to mitigate the greenhouse effect of CO2 and reduce vehicle exhaust emissions has provided the driving force for developing cleaner more efficient vehicle powertrains and environmentally friendly fuels. Reducing consumption of petroleum-derived fuels has become one of the top priorities in the 21st century. As substitutes of the internal combustion engine have yet to overcome technical challenges to attain significant utilisation in the transport sector, the compression ignition diesel engine remains a very attractive powertrain option due to its high thermal efficiency. The International Energy Agency estimates that biofuels can grow to as much as 30% of the world's road transport fuel mix by 2050. Such fuels will include biodiesel and synthetic diesel fuels. In the same frame, alcohols such as bio-ethanol produced from non-food sources with reduced production costs and low CO2 emissions have been proposed as alternative fuels for direct blending with diesel, biodiesel or synthetic diesel. According to Shell, our industrial partner, ethanol made from Brazilian sugar cane produces around 70% lower CO2 emissions from production to use compared to gasoline. Therefore, the potential of ethanol-diesel blends (e-diesel) as alternative fuel for low carbon advanced diesel engines of today and tomorrow has become very important. The use of bio-derived fuel blends such as e-diesel also offers the benefit of compatibility with existing infrastructure.On the other hand, as the complexity of the properties of fuel blends increases, new phenomena that affect engine performance occur in the engine combustion chamber. Thus, improved scientific understanding is essential to overcome potential issues and/or gain potential benefits. One key phenomenon is the micro-explosion of multi-component fuels that is exceedingly possible to occur during spray atomisation and combustion in the case of fuel blends with difference of physical properties among the different fuels in the mixture. The micro-explosion of a miscible multi-component fuel droplet is due to the difference of volatility and boiling point among the different components. For an immiscible multi-component fuel droplet (emulsion droplet as routinely termed), the likelihood of micro-explosion will considerably increase if the lower-boiling-point component cannot dissolve in the mixture and disperse as micro-droplets inside the fuel droplet, such as in the case of e-diesel as the volume fraction of bioethanol increases.Micro-explosion in diesel engines has potentially significant implications on engine performance, combustion and emissions. The phenomenon offers a unique potential in optimising charge preparation in spray combustion systems, making the demands and design of fuel atomisation devices potentially more flexible.However, despite the potentially significant impact, fundamental understanding of the micro-explosion of fuel blends in diesel engines is still lacking. In the present study, we propose for the first time to carry out frontier research using both experimental and modelling techniques to investigate systematically the micro-explosion phenomenon and its effects on spray atomisation and combustion and emissions under realistic diesel engine conditions. The proposed research exploits the creativity that is highly likely to occur at the active interfaces and with the close collaboration between the experimental and modelling researchers with support from Shell which is one of the world's biggest distributors of biofuels. The research outcomes will be disseminated at top international conferences and journals. Development of this science base is vital for the UK to lead the world in advanced technologies of clean, efficient engines and sustainable low CO2 fuels today and tomorrow.