一提到未來推進(jìn)系統(tǒng)，你腦海中首先想到了什么？先進(jìn)燃?xì)獍l(fā)動(dòng)機(jī)、柴油內(nèi)燃機(jī)？還是混合動(dòng)力系統(tǒng)、純電動(dòng)系統(tǒng)？又或是氫燃料電池？事實(shí)上，只要是你說的上來，韓國汽車巨頭現(xiàn)代公司（Hyundai）都有相應(yīng)研發(fā)項(xiàng)目，這種應(yīng)有盡有、全面開花的架勢也贏得了眾多競爭對手的認(rèn)可和尊重。
“我們很榮幸能有機(jī)會(huì)嘗試各種動(dòng)力系統(tǒng)，”現(xiàn)代汽車北美動(dòng)力總成總監(jiān) John Juriga 表示。Juriga 已經(jīng)在現(xiàn)代汽車位于安阿伯市的技術(shù)中心工作 16 年了，他說，“推進(jìn)系統(tǒng)有時(shí)能將我們逼瘋，有時(shí)卻又帶給我們非同尋常的快樂，因?yàn)槲覀冇袡C(jī)會(huì)同時(shí)嘗試幾乎所有可能的推進(jìn)技術(shù)。”
Juriga 表示，內(nèi)燃發(fā)動(dòng)機(jī)仍有“優(yōu)化的余地”，我們有一些關(guān)鍵技術(shù)可以優(yōu)化內(nèi)燃機(jī)的熱力學(xué)、形狀體積和機(jī)械效率等。“現(xiàn)在，擺在我們面前的挑戰(zhàn)是如何更好地整合這些技術(shù)從而實(shí)現(xiàn)我們的優(yōu)化目標(biāo)。如今，各地的排放要求真的越來越難實(shí)現(xiàn)，之前只要求常規(guī)的 NOx 排放物，如今還有 N2O 和顆粒物濃度要求。可以說，正是這些規(guī)定驅(qū)動(dòng)我們不斷優(yōu)化發(fā)動(dòng)機(jī)和推進(jìn)系統(tǒng)架構(gòu)。此外，EPA 現(xiàn)在也要測量“駕駛循環(huán)外排放”（Off-cycle emission），這無疑會(huì)讓我們的工作量翻倍，但同時(shí)也是非常激動(dòng)人心的挑戰(zhàn)。”
美國的排放監(jiān)管環(huán)境近期可能不會(huì)較大改動(dòng)，但現(xiàn)代汽車仍堅(jiān)定不移地執(zhí)行自己的動(dòng)力總成研發(fā)計(jì)劃：密切關(guān)注華盛頓條款的有效期限、加里福尼亞州的 ZEV（零排放車輛）要求，以及與薩克拉門托車輛排放政策配合的第 177 條款。Juriga 斷言，“哪怕聯(lián)邦政府放松監(jiān)管要求，我們的技術(shù)路線圖也不會(huì)改變。”
GDCI 學(xué)習(xí)
汽油內(nèi)燃發(fā)動(dòng)機(jī)“仍將是未來幾十年中的主力選手，但將同時(shí)具備很高的電氣化水平。”Juriga稱，“目前，沒有任何燃料的功率密度比得過汽油。這種老牌動(dòng)力源具有龐大的群眾基礎(chǔ)、成本低廉且效率很高，因此不會(huì)輕易退出歷史舞臺(tái)。在此背景下，我們也集中精力進(jìn)一步提高汽油發(fā)動(dòng)機(jī)的效率，并致力于電氣化和燃燒技術(shù)這兩個(gè)關(guān)鍵領(lǐng)域的發(fā)展。”
Juriga 的團(tuán)隊(duì)屬于韓國現(xiàn)代公司，但同時(shí)也與美國能源部、多家頂尖大學(xué)和供應(yīng)商,及北美市場中的大量排放驗(yàn)證與認(rèn)證機(jī)構(gòu)有直接合作。
現(xiàn)代動(dòng)力總成發(fā)動(dòng)機(jī)開發(fā)測試經(jīng)理 Phil Zoldak 也參加了我們與 Juriga 和 Lee 的會(huì)面。他表示，“我們的先進(jìn)燃燒發(fā)動(dòng)機(jī)研發(fā)主要著力于兩個(gè)領(lǐng)域，第一是繼續(xù)優(yōu)化傳統(tǒng)增壓火花點(diǎn)火發(fā)動(dòng)機(jī)，第二是探索稀薄燃燒發(fā)動(dòng)機(jī)。其中，稀薄燃燒發(fā)動(dòng)機(jī)有兩個(gè)方向，分別為火花點(diǎn)火（借助 EGR 尾氣再循環(huán)和先進(jìn)點(diǎn)火系統(tǒng)）和稀燃?jí)嚎s點(diǎn)火。
“我們更關(guān)注探索稀燃發(fā)動(dòng)機(jī)，重點(diǎn)方向是先進(jìn)的點(diǎn)火、增壓和控制系統(tǒng)，在我們看來，這是解鎖更高燃料效率的關(guān)鍵。”Zoldak 表示，“我們在選擇并優(yōu)化合適的硬件時(shí)大量采用了計(jì)算流體力學(xué) CFD 工具。”
美國能源部在 2011 年至 2018年間贊助了一項(xiàng)名為 GDCI 的項(xiàng)目，專注于壓縮點(diǎn)火汽油發(fā)動(dòng)機(jī)，參與成員包括現(xiàn)代汽車、德爾福（Delphi）和威斯康星發(fā)動(dòng)機(jī)研究咨詢所（Wisconsin EngineResearch Consultants）。Juriga 表示，我們從該項(xiàng)目中學(xué)到了很多，但也同時(shí)面臨兩個(gè)陷阱。“首先，我們必須使用額外的硬件，也就是渦輪增壓器（turbocharger）和機(jī)械增壓器（supercharger）,這毫無疑問會(huì)增加系統(tǒng)的復(fù)雜度和成本。其次，GDCI 發(fā)動(dòng)機(jī)沒有火花點(diǎn)火模式，完全只能靠壓縮點(diǎn)火，因此無法使用冷啟動(dòng)等一系列功能，這可能過于激進(jìn)了。”
“我們的目標(biāo)是使用低成本硬件組件，打造一款可以根據(jù)負(fù)載無縫切換使用火花點(diǎn)火和壓縮點(diǎn)火系統(tǒng)的發(fā)動(dòng)機(jī)。”
混合模式控制器
緊隨 GDCI 項(xiàng)目結(jié)束后開展的是Co-Optima 項(xiàng)目（2019 年 1 月至 2021 年），即“可以滿足未來排放標(biāo)準(zhǔn)的協(xié)同優(yōu)化燃料和多模式汽油壓縮點(diǎn)火發(fā)動(dòng)機(jī)”項(xiàng)目。該項(xiàng)目由美國能源部的“車輛技術(shù)辦公室”資助，旨在打造更加高效的發(fā)動(dòng)機(jī)和燃料搭配組合。目前，全美共有九個(gè)美國國家實(shí)驗(yàn)室參與了這個(gè)項(xiàng)目?，F(xiàn)代北美公司、密歇根理工大學(xué)（MTU 模擬）和 Phillips 66（燃料開發(fā)）也參與了合作。目前，項(xiàng)目的試驗(yàn)臺(tái)正是一款現(xiàn)代 2.2 升柴油發(fā)動(dòng)機(jī)。Juriga 指出，“最終，我們可能研發(fā)出一款擁有獨(dú)一無二氣缸頭的燃?xì)獍l(fā)動(dòng)機(jī)。”
“我們希望通過該項(xiàng)目實(shí)現(xiàn)高級(jí)別的整合，并最終在盡量使用現(xiàn)成硬件的基礎(chǔ)上實(shí)現(xiàn)量產(chǎn)，”Zoldak 解釋道，“這款發(fā)動(dòng)機(jī)將能夠以火花點(diǎn)火（SI）模式啟動(dòng)，化學(xué)計(jì)量或稀燃模式運(yùn)行，并借助內(nèi)部 EGR 系統(tǒng)轉(zhuǎn)換至低溫燃燒模式，然后使用外部 EGR 系統(tǒng)再次轉(zhuǎn)換為壓縮點(diǎn)火模式。因此，隨著負(fù)載的不斷增加，你可以選擇三種過渡模式。
Juriga 指出，“不難想象，這種復(fù)雜的模式切換并不容易，燃料的辛烷值也會(huì)產(chǎn)生影響。” Phillips 66 公司提供一系列不同辛烷值和反應(yīng)性的燃料。然后，我們會(huì)在項(xiàng)目中對這些燃料進(jìn)行建模。Zoldak 表示，“我們正在使用密歇根科技大學(xué)開發(fā)的真實(shí)燃料建模技術(shù)。”
Co-Optima 項(xiàng)目旨在首先通過結(jié)合合適的模擬和硬件以實(shí)現(xiàn)穩(wěn)態(tài)性能，然后解決幾乎每臺(tái)稀燃發(fā)動(dòng)機(jī)都需要面對的挑戰(zhàn)，即優(yōu)化駕駛體驗(yàn)。
“我們正在構(gòu)建一個(gè)可以在定點(diǎn)或動(dòng)態(tài)過程中捕捉所有模式的發(fā)動(dòng)機(jī)，”Zoldak 解釋說。“這個(gè)項(xiàng)目的重點(diǎn)不在瞬態(tài)測試，但也不是說一點(diǎn)瞬態(tài)測試也不會(huì)有。比如，使用混合模式控制器處理不同區(qū)域，然后針對每個(gè)區(qū)域進(jìn)行校準(zhǔn)優(yōu)化，并使用算法在不同模式間切換。”
模式切換的實(shí)現(xiàn)關(guān)鍵在于開發(fā)團(tuán)隊(duì)對系統(tǒng)動(dòng)態(tài)的理解和掌握，即如何協(xié)調(diào)利用不同模式的工作速度，以及如何進(jìn)行調(diào)整使發(fā)動(dòng)機(jī)能夠根據(jù)命令迅速開始工作，而非只關(guān)注噴射器、EGR 閥和渦輪增壓水平等硬件規(guī)格。Juriga 指出，“我們想看看，我們到底能稀薄到什么程度以及需要哪些燃料和空氣系統(tǒng)。”此外，本項(xiàng)目的副線之一是研究新的點(diǎn)火系統(tǒng)與技術(shù)。
“我們將在開發(fā)過程中改進(jìn)壓燃式汽油發(fā)動(dòng)機(jī)的特性，以減少汽缸排放，”Juriga 指出，“燃?xì)夂筒裼图夹g(shù)的融合是我們多年來一直關(guān)注的問題。”
Name a future propulsion solution for vehicles, and Hyundai's on it. From advanced gas and diesel ICE, to all manner of hybrid, EV, and hydrogen fuel cell, Korea's mobility king has it in development or in production. Competitors acknowledge their respect for the company's rapid progress on all engine fronts in recent years.
"We're fortunate to be working on everything," asserts a modest John Juriga, Hyundai North America's Director of Powertrain, who has been with the company's Ann Arbor technical center for 16 years. "It drives us crazy sometimes, but it's also incredibly fun because we're developing all these different technologies concurrently.”
There are still "knobs to turn”— the key technologies that can improve the thermodynamic, volumetric, and mechanical efficiency of combustion engines, he says. "The challenge for us is how to integrate all these systems to do that. Emission requirements are getting really, really tough—standard NOx, and now N2O and particulates. They're huge in driving the engine and propulsion system architecture. And EPA now is looking at off-cycle emissions. The complexity of what we have to accomplish is multiplied, but it's an exciting time.”
That U.S. regulatory environment may seem to be in a ‘holding pattern' but Hyundai remains unwavering in its powertrain plans: keeping an eye on both Washington's regulatory tenor and also on California, with its ZEV [zero-emission vehicle] requirements, along with the Section 177 states aligned with Sacramento's mobile-emissions policies. "Even if the federal government relaxes its regulations, our technology roadmap won't change," Juriga asserted.
The gasoline ICE "will remain the mainstay for decades to come—but it's going to have high levels of electrification attached," asserts Juriga. "There is nothing that currently compares to the power density of gasoline as a fuel source. And the combination of its prevalency, low cost and efficiency means it's not going to go away quickly. So, we focus on how to make it more efficient. That's why electrification and combustion development are two key areas we're working on.”
While it operates under the umbrella of Hyundai Powertrain in Korea, Juriga's team engages in collaborative R&D projects with the U.S. Dept. of Energy (DoE), net- working with top universities and suppliers, in addition to spearheading North American market emissions validation and certification.
"In advanced combustion engines there are two main areas that we're involved in," notes Phil Zoldak, Hyundai Powertrain's manager of engine development and testing, who joined our meeting with Juriga and Lee. "One is furthering traditional boosted SI engines. The other is lean-burn engines, and within that space are two branches: Spark-ignited, which looks at dilution with EGR and advanced ignition systems, and lean-burn compression ignition.
"We're focusing more on the lean-burn development side, in what we call Technology Enablers—advanced ignition systems, advanced boosting and controls," he said. "We use CFD extensively to co-optimize and select the right hardware.”
A DoE-sponsored program that ran from 2011 to 2018, dubbed GDCI, focused on a gasoline-fueled compression-ignition engine with Hyundai working with partners Delphi and the Wisconsin Engine Research Consultants. It yielded significant learnings, Juriga said, but had two pitfalls. "The hardware we had to use—a turbocharger and supercharger—drove system complexity and cost. It also had no spark mode; it relied exclusively on compression ignition, which compromised things like cold start. It was perhaps too aggressive.”
"The intent is to create an engine that seamlessly transitions from spark-ignition stoichiometry to compression-ignition mode, depending on load, using low-cost hardware."
GDCI was followed by the Co-Optima Initiative, launched in January 2019 and running to 2021. Co-Optima is short for "Co-optimized Fuel and Multi-Mode Gasoline Compression-Ignition Engine for Meeting Future Emission Standards."Funded by the DoE's Vehicle Technology Office, the program aims to create engines and fuels that are more effectively optimized together. Nine U.S. National Labs are collaborating on the project. Hyundai North America is collaborating with Michigan Technological University (MTU - simulation) and Phillips 66 (fuel development). A Hyundai 2.2-L diesel is serving as a mule test rig; "we may end up with a gas engine in the end, with a unique head geometry," Juriga noted.
"This program is our effort to put everything into a package that is production-intent and uses more off-the-shelf-type hardware," explained Zoldak. "The engine has the ability to start out in an SI mode, operating in a stoichiometric or lean-combustion mode, and transition into a more low-temperature combustion mode using internal residuals [EGR]. Then make another transition into a compression- ignition mode using external EGR. So, there's three transitional modes we're looking at as you increase load.
"The complexity of mode switching comes into play, and as you can imagine fuel octane starts to bear on this," Juriga noted. Phillips 66 is providing a range of fuels with different octanes and reactivity. The fuels are then being modeled; "we're using a real-fuel modeling technique that MTU has developed," said Zoldak.
The program aims to achieve steady-state performance first, combining simulation and hardware selection, before trying to tackle the transients that have challenged the drivability of virtually every lean-burn engine development effort.
"We're building an engine that can capture all the modes, at specific points, on the dyno," Zoldak explained. "The main scope of the work wasn't to do transient testing. It wasn't a requirement of the project, but we'll be doing some testing in transients. We'll handle them using a mixed-mode controller—we have different combustion modes that are calibration-optimized for that region and use algorithms to transition from one mode to another.”
The changeovers will be dependent on the development team's grasp of system dynamics—the operating-speed deltas among production-intent, rather than R&D-spec hardware including injectors, EGR valves, turbo boost levels, etc.—and how they can be adjusted to operate rapidly, on command. "We'll look at how lean can we go, and what fuel and air systems do we need to support it.”Juriga noted. New ignition-system technologies are being investigated as a sideline of the project.
"As we go through development, we'll be refining the characteristics of the compression-ignition gasoline engine with the goal of reducing emissions in cylinder," he explained. "The merging of gas and diesel technologies is something we've been looking at for years.”
SAE Automotive Engineering
準(zhǔn)備啟動(dòng)測試：Phil Zoldak（左）和 John Juriga 正在對一款稀燃發(fā)動(dòng)機(jī)進(jìn)行測試前的最終檢查。
盡管如今的推進(jìn)系統(tǒng)解決方案越來越復(fù)雜，但作為一名將發(fā)動(dòng)機(jī)研發(fā)融入血液的動(dòng)力系統(tǒng)“老兵”，John Juriga 仍深深被這個(gè)領(lǐng)域所吸引。