在底特律舉行的SAE 2017 高效內(nèi)燃發(fā)動機研討會（SAE 2017 High-Efficiency IC Engines Symposium）上，德爾福公司預測，如果發(fā)動機采用公司的第三代汽油直噴壓燃（GDCI）系統(tǒng)，可將熱效率提升至42%左右，超過目前任何量產(chǎn)汽油發(fā)動機的水平（40%）。
德爾福先進傳動系統(tǒng)工程經(jīng)理Mark Sellnau表示，目前公司的第三代GDCI燃燒系統(tǒng)正在研發(fā)之中，未來采用這種系統(tǒng)的發(fā)動機的熱效率將比當下的常規(guī)火花點火式直噴汽油發(fā)動機高22%，比2L的柴油發(fā)動機高11%。他說，德爾福已經(jīng)克服了GDCI燃燒系統(tǒng)早期面臨的很多挑戰(zhàn)，公司相信這種技術(shù)可以讓低溫燃燒系統(tǒng)的排放達到美國環(huán)保署Tier 3 Bin 30水平。
具體來說，德爾福第二代GDCI系統(tǒng)的重大升級，包括“wetless”燃燒技術(shù)、更快的冷啟動運行速度，以及優(yōu)化的低溫尾氣處理系統(tǒng)（可在大約4s內(nèi)轉(zhuǎn)換90%的一氧化碳）。
Sellnau表示，第三代系統(tǒng)的壓縮比已從之前的15：1提升至16：1，活塞沖程更長，上止點間隙也更大，可以保證德爾福的“wetless”運行目標，確保燃料在接觸氣缸或燃燒室內(nèi)壁表面時能夠充分汽化。系統(tǒng)先進燃料噴射器的工作壓強為350 bar (5076 psi)，可以實現(xiàn)“三次噴射”。Sellnau表示，這里所說的第三次噴射“就是GDCI燃燒系統(tǒng)與HCCI（均質(zhì)壓燃）系統(tǒng)拉開差距的地方。”
德爾福的GDCI研發(fā)受到美國能源部一項為期4年、總規(guī)模達980萬美元項目的資助，項目合作伙伴包括橡樹嶺國家實驗室（Oak Ridge National Laboratory）、Umicore，及威斯康星大學麥迪遜分校。
除了最新研發(fā)的低溫催化劑技術(shù)外，該系統(tǒng)還將采用多種減排措施，包括進氣口加熱裝置、汽油微粒過濾器及尿素噴射系統(tǒng)等。Sellnau相信，憑借上述這些措施，再加上第三代系統(tǒng)的先進燃燒設(shè)計，采用GDCI燃燒系統(tǒng)的發(fā)動機一定可以達到Tier 3 Bin 30規(guī)定的要求，從而在很大程度上保證了這種系統(tǒng)能夠?qū)崿F(xiàn)量產(chǎn)。
此外，Sellanu承諾，最新GDCI系統(tǒng)對汽油沒有特殊要求，目前常用汽油的辛烷值水平就沒有問題。他說，“我們要打入市場，就必須能夠直接使用市場中現(xiàn)行的油品。”
Sellanu說，項目團隊從2017年2月份就開始為第三代GDCI系統(tǒng)收集測試結(jié)果，“未來，我們將看到一款非常高效的發(fā)動機一點點豐滿起來，并最終加入我們的汽車項目。”不過，Sellanu并未預測該系統(tǒng)具體將于何時登陸量產(chǎn)發(fā)動機。
Delphi projects that engines employing its coming third-generation gasoline direct-injection compression-ignition (GDCI) combustion system will attain a thermal efficiency of 42%, the company said at the 2017 SAE High-Efficiency IC Engines Symposium in Detroit. That thermal efficiency would top any current production-vehicle gasoline engine, the most efficient of which are claimed to have peak thermal efficiency of about 40%.
Mark Sellnau, engineering manager, Delphi Advanced Powertrain, said a gasoline engine using the third-generation GDCI system now under development is projected to have approximately 22% better thermal efficiency than a current conventional spark-ignited gasoline engine with direct fuel injection and 11% better than a 2L diesel engine. He said many of the initial engineering challenges for GDCI have been overcome and that the company believes it can make the low-temperature combustion system emissions-compliant at the EPA Tier 3, bin 30 level.
Major advances over Delphi’s second-generation GDCI system include “wetless” combustion, quicker cold-start operation and an optimized low-temperature exhaust aftertreatment that achieves roughly 90% carbon monoxide conversion in about 4s.
Sellnau said the third-generation system has increased the compression ratio to 16:1 (from 15:1) and its new longer stroke and increased top-dead-center piston clearance enable the wetless operation that sees fuel completely vaporized before it contacts cylinder or combustion-chamber surfaces. Advanced fuel injectors operate at 350 bar (5076 psi) and provide three injection events. The third injection, Sellnau said, is “what differentiates (GDCI) from HCCI (homogenous-charge compression ignition).”
Much of Delphi’s GDCI research is being conducted under the auspices of a four-year, $9.8-million program funded by the U.S. Department of Energy; Delphi’s partners in the project include Oak Ridge National Laboratory, Umicore and the University of Wisconsin-Madison.
The system will require a variety of emissions-reduction measures that, in addition to the newly-formulated low-temperature catalyst, include an intake-air heater, gasoline particulate filter and urea injection. But Sellnau was confident those measures, coupled with the combustion-related design advances of the third-generation system, will enable a production engine to be Tier 3, bin 30 compliant—a vital achievement to advance the system for production-vehicle readiness.
Moreover, he promised the latest GDCI will operate with gasoline at currently-available octane. “We really need to get to market with commercial gasoline,” he said.
Sellanu said the project team began gathering test results for the third-generation GDCI system in February 2017 and added, “I think we’re going to see a very efficient engine evolving and going into our vehicle program.” He did not, however, provide a projection on when the system might be fitted to a production-vehicle engine.
Author: Bill Visnic
Source: SAE Automotive Engineering Magazine
這款測試發(fā)動機安裝了一款較早版本的德爾福GDCI燃燒系統(tǒng)。
一款早期GDCI發(fā)動機燃燒室的渲染圖。
