利用生物柴油产量的不断提高，设计人员正规划新战略（美国国家生物柴油委员会）

在过去100年来，内燃机燃油一直没有什么重大的变化，但今后就说不一定了。生物燃油研究不断取得进展，非公路商用车工程师开发的新技术使发动机能够使用各种不同的混合燃油。

生物燃油方面采取的大量行动，但是在从替代能源跃升为主流能源的竞赛中，生物燃油却落后于天然气。根据美国环保局（EPA）的消息，去年美国的炼油厂生产出大约17亿加仑（约合64亿升）的生物柴油。发动机开发商及整个供应链也正努力开发新技术，试图让所有型号的发动机能够使用任意调和的生物燃油。

美国西南研究院发动机、排放及车辆研究首席工程师Bapi Surampudi说道：“替代燃油的使用存在的最大问题是校准。要使成本最小化，通常就需要在多个平台上重复使用相同的电子设备。因此，难点之一就是要设计出一套能够适应各种情况的电子架构（包括硬件和软件）。”

研究人员正尝试使用不同的技术，测试如果才能高效地检测出可用燃油的成份。其中一个策略就是将测量燃油的传感器放在油箱内，另一种方案是利用燃烧控制系统实时检测向发动机输送的燃油。

博格华纳先进工程团队高级技术专家Chris Mays介绍道：“对于有自力推进的交通工具来说，可以通过油箱内燃油成分检测分析，在每次加油时进行“重新调整”或校正，或者也可以进行实时检测。这就意味着，OEM就需要决定是监测燃油本身还是燃烧过程。如果是监测燃烧，不管是直接还是间接测量，我们都将获得大量的数据反馈，获得发动机组件、系统及燃油变量。”

计算机能力的迅猛发展也将帮助工程师和程序规划师能够高效地对燃油进行分析。

里卡多（Ricardo）混合动力及电气系统营业部总监Ali Maleki说道：“电子控制装置的性能越来越好，燃烧过程的控制也就越来越精确，替代燃油发动机的故障率也就相应的减少。新的电子技术可以更好的控制排放、废气再循环并精确供油。在固定设备、火车和货车等对运营成本较敏感的领域，使用替代燃油将是一个非常重要的趋势。”

随着控制系统的发展，越来越多的生物燃油都开始投入生产，工程师将公不断致力于让每一滴燃油都发挥最大作用。

Surampudi说：“发动机制造商必须掌握各种生物燃油的优势与缺点，同时在更快、更复杂的测试中不断积累经验。”

我们对生物燃料的了解，很大一部分认知是来源于建模与仿真。燃烧过程是很复杂的，细微的变化就会产生巨大的不同，所以必须要用大量的测试来提高效率。

Mays说道：“传感器的信号是最需要考虑的问题，设计阶段模拟感应器反馈有助于得到良好的信噪反馈。比如在这个过程可以分析传感器可以在液流中的状态，确保感应器探测到各种气体混合状态，浓度是否足以进行冷凝等信息。”

作者:Terry Costlow

Designers are devising new strategies to utilize the growing output of biodiesel. (National Biodiesel Board)

Fuel for combustion engines has not transformed significantly over the past 100 years, but things may change. Biofuel research continues to advance as off-highway engineers develop new techniques that will let engines run on varying mixtures.

There’s plenty of activity in biofuels, though they trail natural gas in the race to make the leap from alternative energy source to mainstream fuel. U.S. refiners produced around 1.7 billion gallons (6.4 billion L) of biodiesel fuel last year, according to the U.S. EPA. Engine developers throughout the supply chain are working on techniques that let operators run with any mix of fuels on any engine model.

“The adoption of alternative fuels is a calibration issue,” said Bapi Surampudi, Principal Engineer for Engine, Emissions, and Vehicle Research at theSouthwest Research Institute. “To minimize cost, the goal has always been to re-use the same electronics in multiple platforms. Therefore, one challenge is to design a common electronic architecture (hardware and software) that works in all cases.”

Researchers are exploring different techniques to efficiently determine the makeup of fuel being used. One strategy is to add sensors that measure fuel in the tank, while another leverages combustion control systems to monitor fuel as it’s fed to the engine.

“For self-propelled vehicles, the detection could be a tank-based analysis and a ‘retune’ or correction method every time the tank is filled,” said Chris Mays, Senior Technical Specialist at BorgWarner’s Advance Engineering Group. “The sensing method could also be continuous. In this case, OEMs need to determine whether to measure the fuel or the combustion. Measuring the combustion, either directly or indirectly, provides the greatest payback as it accounts for engine component and system variation as well as fuel variation.”

The rapid advance in computing power is helping engineer and programmers analyze fuels efficiently.

“Higher performance electronic control units enable a more precise control of the combustion process and reduced penalty efficiency of the alternative fuel engine,” said Ali Maleki, Business Unit Director for Hybrid and Electrical Systems, Ricardo. “New electronic technologies are embedded for better emissions control, gas recirculation control, precise fuel delivery. There is significant trend for alternative fuels in the stationary, railway, and truck applications that are more operating-cost sensitive.”

As control systems evolve and more biofuels move into production, engineers are continuously striving to eke more work from every drop of fuel.

“Engine manufacturers must become knowledgeable of the potential and the drawbacks of different biofuels and gain experience through faster and more sophisticated testing,” Surampudi said.

Much of that knowledge will be gained through modeling and simulation. Combustion is very complex, with major differences arising from minor changes, so many tests must be run to improve efficiency.

“Getting good signals at the sensors is one aspect to consider,” Mays said. “Simulating sensor responses in the design phase can help give good signal-to-noise response. This can include analysis of sensors in the gas flow stream to make sure they are sensing well-mixed gases and are robust to condensate, for example.”

Author: Terry Costlow