利用生物柴油產量的不斷提高，設計人員正規劃新戰略（美國國家生物柴油委員會）
在過去100年來，內燃機燃油一直沒有什么重大的變化，但今后就說不一定了。生物燃油研究不斷取得進展，非公路商用車工程師開發的新技術使發動機能夠使用各種不同的混合燃油。
生物燃油方面采取的大量行動，但是在從替代能源躍升為主流能源的競賽中，生物燃油卻落后于天然氣。根據美國環保局（EPA）的消息，去年美國的煉油廠生產出大約17億加侖（約合64億升）的生物柴油。發動機開發商及整個供應鏈也正努力開發新技術，試圖讓所有型號的發動機能夠使用任意調和的生物燃油。
美國西南研究院發動機、排放及車輛研究首席工程師Bapi Surampudi說道：“替代燃油的使用存在的最大問題是校準。要使成本最小化，通常就需要在多個平臺上重復使用相同的電子設備。因此，難點之一就是要設計出一套能夠適應各種情況的電子架構（包括硬件和軟件）。”
研究人員正嘗試使用不同的技術，測試如果才能高效地檢測出可用燃油的成份。其中一個策略就是將測量燃油的傳感器放在油箱內，另一種方案是利用燃燒控制系統實時檢測向發動機輸送的燃油。
博格華納先進工程團隊高級技術專家Chris Mays介紹道：“對于有自力推進的交通工具來說，可以通過油箱內燃油成分檢測分析，在每次加油時進行“重新調整”或校正，或者也可以進行實時檢測。這就意味著，OEM就需要決定是監測燃油本身還是燃燒過程。如果是監測燃燒，不管是直接還是間接測量，我們都將獲得大量的數據反饋，獲得發動機組件、系統及燃油變量。”
計算機能力的迅猛發展也將幫助工程師和程序規劃師能夠高效地對燃油進行分析。
里卡多（Ricardo）混合動力及電氣系統營業部總監Ali Maleki說道：“電子控制裝置的性能越來越好，燃燒過程的控制也就越來越精確，替代燃油發動機的故障率也就相應的減少。新的電子技術可以更好的控制排放、廢氣再循環并精確供油。在固定設備、火車和貨車等對運營成本較敏感的領域，使用替代燃油將是一個非常重要的趨勢。”
隨著控制系統的發展，越來越多的生物燃油都開始投入生產，工程師將公不斷致力于讓每一滴燃油都發揮最大作用。
Surampudi說：“發動機制造商必須掌握各種生物燃油的優勢與缺點，同時在更快、更復雜的測試中不斷積累經驗。”
我們對生物燃料的了解，很大一部分認知是來源于建模與仿真。燃燒過程是很復雜的，細微的變化就會產生巨大的不同，所以必須要用大量的測試來提高效率。
Mays說道：“傳感器的信號是最需要考慮的問題，設計階段模擬感應器反饋有助于得到良好的信噪反饋。比如在這個過程可以分析傳感器可以在液流中的狀態，確保感應器探測到各種氣體混合狀態，濃度是否足以進行冷凝等信息。”
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
