2015年1月1日，美國(guó)環(huán)保署（EPA）正式宣布有關(guān)Tier 4 Final發(fā)動(dòng)機(jī)的環(huán)保法規(guī)，開始執(zhí)行針對(duì)額定功率超過750hp （560kW）柴油發(fā)動(dòng)機(jī)的新排放規(guī)定，這標(biāo)志著高功率（HHP）發(fā)動(dòng)機(jī)技術(shù)新紀(jì)元的到來。達(dá)到微粒（PM）與氮氧化物（NOx）排放的最低限值要求，是當(dāng)今HHP發(fā)動(dòng)機(jī)制造商必須解決的最重要的技術(shù)問題。
每一次排放法規(guī)的更新，都提出了清晰的減排目標(biāo)，但是即便法規(guī)再嚴(yán)格，康明斯也總能設(shè)計(jì)出性能更高、運(yùn)行成本更低的發(fā)動(dòng)機(jī)。從Tier 4 Final發(fā)動(dòng)機(jī)研發(fā)工作啟動(dòng)伊始，康明斯就致力于設(shè)計(jì)出比當(dāng)今北美主流的Tier 2發(fā)動(dòng)機(jī)性能更為優(yōu)越的產(chǎn)品，并同時(shí)有效降低發(fā)動(dòng)機(jī)的總擁有成本。為了達(dá)到這一目標(biāo)，我們的工程團(tuán)隊(duì)努力了解顧客對(duì)于HHP發(fā)動(dòng)機(jī)應(yīng)用的要求，而這些寶貴的信息為我們的Tier 4 Final技術(shù)研發(fā)作出了重要貢獻(xiàn)。
如今，康明斯非常自豪的宣布，我們的Tier 4 Final HHP發(fā)動(dòng)機(jī)技術(shù)研發(fā)已經(jīng)完成，而且超越了項(xiàng)目的最初目標(biāo)。燃油節(jié)約可達(dá)4%，大修前使用壽命延長(zhǎng)了10%，最重要的是，發(fā)動(dòng)機(jī)的正常運(yùn)行時(shí)間毫不遜色于目前任何一款康明斯HHP發(fā)動(dòng)機(jī)。
這一結(jié)論不僅來自于實(shí)驗(yàn)室數(shù)據(jù)，我們還進(jìn)行了長(zhǎng)達(dá)6萬小時(shí)的各種路上實(shí)測(cè)，這使得康明斯得以實(shí)現(xiàn)其承諾——按OEM的生產(chǎn)計(jì)劃，為其提供動(dòng)力更強(qiáng)勁的發(fā)動(dòng)機(jī)。根據(jù)這些路上實(shí)測(cè)的優(yōu)異結(jié)果，我們可以將Tier 4 Final發(fā)動(dòng)機(jī)的生產(chǎn)啟動(dòng)時(shí)間調(diào)整至排放法規(guī)生效日之前。這意味著QSK19、QSK50、QSK60和QSK95等型號(hào)的康明斯發(fā)動(dòng)機(jī)將成為業(yè)內(nèi)第一批上市的Tier 4 Final發(fā)動(dòng)機(jī)。
康明斯提供的，不僅僅是全行業(yè)的第一批Tier 4 Final發(fā)動(dòng)機(jī)產(chǎn)品。整個(gè)Tier 4 Final研發(fā)項(xiàng)目的目標(biāo)是在不增加排量、不改變發(fā)動(dòng)機(jī)速率的情況下實(shí)現(xiàn)極低的排放，并同時(shí)保持或達(dá)到更高的功率輸出水平?？得魉筎ier 4 HHP發(fā)動(dòng)機(jī)的外型與Tier 2發(fā)動(dòng)機(jī)一模一樣，但在內(nèi)部做了很多改進(jìn)，包括提高廢氣閥的渦輪增壓性能以提高瞬態(tài)響應(yīng)能力，調(diào)整活塞凹坑的設(shè)計(jì)以提高燃燒的清潔度等，而發(fā)動(dòng)機(jī)的核心設(shè)計(jì)則基本保持不變。
穩(wěn)健的技術(shù)
Tier 4 Final發(fā)動(dòng)機(jī)研發(fā)項(xiàng)目的驅(qū)動(dòng)力來自康明斯的核心理念——通過我們所掌握的新技術(shù)或現(xiàn)有技術(shù)、系統(tǒng)和現(xiàn)有部件的改進(jìn)，滿足HHP應(yīng)用的耐久性與可靠性要求。我們稱其為“值得信賴的創(chuàng)新。”
為滿足這些要求，我們選擇將柴油發(fā)動(dòng)機(jī)業(yè)內(nèi)最為嚴(yán)苛的應(yīng)用工況，即大型采礦挖掘機(jī)的運(yùn)行條件作為研發(fā)的起點(diǎn)。這些采礦挖掘機(jī)在運(yùn)轉(zhuǎn)時(shí)通常負(fù)載系數(shù)達(dá)到75%，每年工作時(shí)間長(zhǎng)達(dá)8000小時(shí)，對(duì)發(fā)動(dòng)機(jī)施加的時(shí)間負(fù)荷之長(zhǎng)，沖擊載荷之大，非任何其他機(jī)械可以相比。因此，這一極端的負(fù)載循環(huán)就成為了我們模擬所采用的基數(shù)。如果我們的Tier 4 Final發(fā)動(dòng)機(jī)可以承受采礦挖掘機(jī)的工況要求，就能在其他所有應(yīng)用要求下表現(xiàn)出色。
康明斯Tier 4 Final發(fā)動(dòng)機(jī)系統(tǒng)還有一些其他的優(yōu)勢(shì)。它的維修保養(yǎng)周期延長(zhǎng)到500小時(shí)，為Tier 2發(fā)動(dòng)機(jī)的兩倍。我們還將發(fā)動(dòng)機(jī)的大修前使用壽命提升了10%，這意味著以2850 hp（2125 kW）功率運(yùn)行的Tier 4 Final QSK60發(fā)動(dòng)機(jī)可以在大修前持續(xù)燃燒1,100,000加侖（4,200,000升）燃油，具體視負(fù)載循環(huán)而定。
為提高發(fā)動(dòng)機(jī)的可靠性，我們的設(shè)計(jì)團(tuán)隊(duì)分析了Tier 4 Final發(fā)動(dòng)機(jī)中所有可能導(dǎo)致非計(jì)劃內(nèi)停工的潛在風(fēng)險(xiǎn)，并采取措施加以預(yù)防?？得魉剐麻_發(fā)的NanoNet過濾介質(zhì)就是一個(gè)很好的例子。這個(gè)用于燃油濾清器的介質(zhì)專為實(shí)現(xiàn)超高燃油潔凈度并隔離灰塵而設(shè)計(jì)。與傳統(tǒng)介質(zhì)相比，這一新介質(zhì)的孔徑更為均一，能夠捕獲并過濾掉更多的有害物質(zhì)顆粒，從而提升保護(hù)效果。
與Tier 2發(fā)動(dòng)機(jī)相比，Tier 4 Final發(fā)動(dòng)機(jī)在設(shè)計(jì)之初已將大規(guī)模改造問題考慮在內(nèi)，因此它們可以輕松承受三次大修。這一舉措的另一大好處是，發(fā)動(dòng)機(jī)無需在使用壽命的中期進(jìn)行任何重大維修。Tier 4 Final發(fā)動(dòng)機(jī)在實(shí)現(xiàn)極低排放標(biāo)準(zhǔn)的同時(shí)，竟然能夠同時(shí)達(dá)到如此高水平的耐久性和性能提升，這超出了絕大多數(shù)業(yè)內(nèi)人士的預(yù)期。
實(shí)現(xiàn)極低排放水平
對(duì)Tier 4 Final HHP發(fā)動(dòng)機(jī)而言，微粒的去除主要是通過在氣缸內(nèi)利用高壓實(shí)現(xiàn)多次燃油噴射完成的，而氮氧化物的去除則主要是通過SCR后處理技術(shù)在尾氣部分實(shí)現(xiàn)。缸內(nèi)清除微粒與將氮氧化物排出發(fā)動(dòng)機(jī)的技術(shù)，可以簡(jiǎn)化減排策略，并充分實(shí)現(xiàn)發(fā)動(dòng)機(jī)的潛力。
此外，由于無需在氣缸內(nèi)清除氮氧化物，為降低燃耗而設(shè)計(jì)的燃燒方程式便得到了極大的寬裕度。該方程式還允許發(fā)動(dòng)機(jī)在更高的負(fù)載系數(shù)下運(yùn)行，但同時(shí)氣缸壓力與活塞速度要求則更為寬松。
SCR后處理技術(shù)的優(yōu)勢(shì)在發(fā)動(dòng)機(jī)行業(yè)早已廣為人知?，F(xiàn)在SCR已在所有75-750 hp （56 to 560 kW）級(jí)別的Tier 4 Final發(fā)動(dòng)機(jī)以及北美洲所有的公路卡車發(fā)動(dòng)機(jī)上得到了應(yīng)用。在北美，康明斯的SCR技術(shù)已在超過100萬臺(tái)發(fā)動(dòng)機(jī)上成功應(yīng)用，重復(fù)證明了該技術(shù)的成功。人們清楚地知道，沒有其他任何技術(shù)可以在確保極低排放的同時(shí)，使發(fā)動(dòng)機(jī)達(dá)到如此優(yōu)越的性能和燃油節(jié)約水平。
只有康明斯可以將SCR技術(shù)應(yīng)用到馬力高達(dá)4400 hp (3280 kW)的HHP發(fā)動(dòng)機(jī)上。我們自行設(shè)計(jì)、生產(chǎn)并整合SCR系統(tǒng)，充分利用康明斯在催化轉(zhuǎn)換效率、柴油機(jī)尾氣處理液（DEF）噴霧模式噴射、以及整合控制邏輯方面的專業(yè)知識(shí)，專門為HHP發(fā)動(dòng)機(jī)開發(fā)了下一代SCR系統(tǒng)。
SCR要求使用DEF引發(fā)催化劑的化學(xué)反應(yīng)。DEF的使用和儲(chǔ)藏都非常方便，供應(yīng)豐富，并有助于節(jié)省燃油。由于使用了DEF，Tier 4 Final發(fā)動(dòng)機(jī)能夠使用更高級(jí)的燃燒優(yōu)化技術(shù)以提高發(fā)動(dòng)機(jī)效率，并通過SCR后處理技術(shù)降低尾氣氮氧化物排放量，從而使節(jié)油量得到提升。這一優(yōu)化成果可以降低燃油和DEF的總消耗量，幫助客戶節(jié)省大約3%的總?cè)加统杀尽?/p>
通過這樣的方法，康明斯選擇的技術(shù)變革方向可以為運(yùn)行商大大節(jié)約成本，因?yàn)檫@種程度的燃油節(jié)省量，對(duì)大排量發(fā)動(dòng)機(jī)而言是非常優(yōu)異的。
康明斯Tier 4 Final發(fā)動(dòng)機(jī)還有更多其他優(yōu)勢(shì)，例如每小時(shí)可移動(dòng)更多噸位，以及可在更短時(shí)間到達(dá)扭矩峰值扭矩等。事實(shí)證明，這些優(yōu)勢(shì)使得發(fā)動(dòng)機(jī)能在最嚴(yán)苛的循環(huán)工況以及最高的負(fù)載系數(shù)下實(shí)現(xiàn)巔峰性能。我們確信至今仍未有任何HHP發(fā)動(dòng)機(jī)具備比康明斯Tier 4 Final更優(yōu)越的性能， 這一切都使得我們的Tier 4 Final技術(shù)更令人信服。
由康明斯高馬力發(fā)動(dòng)機(jī)工程副總裁Jim Trueblood專為《SAE非公路車輛工程（ SAE Off-Highway Engineering）》期刊撰寫。
Innovation is at the core of engine design
A new era in high horsepower (HHP) engine technology began on January 1, 2015, the official start date of the U.S. Environmental Protection Agency’s (EPA) Tier 4 Final emissions regulations for diesel engines rated above 750 hp (560 kW). Meeting these very low limits for particulate matter (PM) and oxides of nitrogen (NOx) emissions is the most significant technical challenge that HHP engine manufacturers have faced to date.
With every emissions regulations change, there is a clear target to reduce emissions, but for Cummins, there is always the opportunity to deliver engines with even higher performance and lower operating costs. From the start of our Tier 4 Final development program, Cummins has been committed to delivering engines that surpass the performance levels of the Tier 2 engine population operating in North America today with a lower total cost of ownership. With this goal in mind, our engineering teams went out and captured customer needs for our HHP engine applications and that valuable input went on to inspire our Tier 4 Final technology.
Cummins is very pleased to report that our Tier 4 Final HHP technology has achieved—and surpassed—our original goals for the program, providing fuel savings of up to 4%, extending life-to-overhaul by 10% and—most importantly—enabling engine uptime availability equal to that of any Cummins HHP engine in service today.
Our results were validated not only in the test cell, but also through an extensive series of field tests approaching 60,000 hours, which has enabled Cummins to remain consistent in keeping our promise to deliver more productive engines on schedule for OEM introductions. Based on the impressive results from our field tests, we were able to move the start of our Tier 4 Final engine production ahead of the emissions effect date. This means that Cummins engines such as the QSK19, QSK50, QSK60, and QSK95 will be the first Tier 4 Final HHP engines operating in the industry.
Not only is Cummins able to provide the first Tier 4 Final engines for the industry, Cummins Tier 4 Final approach also means our engines achieve very low emissions levels with no increase in engine displacement needed, no change to engine ratings, and the same, or even improved, power delivery. Each Cummins Tier 4 HHP engine also offers a near identical envelope to that of its Tier 2 predecessor. Upgrades include more efficient wastegate turbocharging to improve transient response and a revised piston bowl design for cleaner combustion, but the base engine is essentially the same.
Robust technology
Our Tier 4 Final program was driven with Cummins core philosophy to utilize new or improved technologies, systems, and components we knew would meet the durability and reliability levels demanded for tough HHP applications. We call this "Innovation You Can Depend On."
To meet these criteria, we took the most severe application in the diesel engine industry—large mining excavators typically operating at 75% load factors for as many as 8000 hours per year—as a starting point. No other machines put more stress or shock load on the engine for more hours. As a result, this extreme duty cycle became our simulation base point. If our Tier 4 Final technology could be counted upon to endure the operating conditions of a mining excavator, we knew it would do well in every other application.
Cummins Tier 4 Final engine systems also provide some other advantages. Service intervals are extended to 500 hours, twice that of the Tier 2 engines. Engine life-to-overhaul is increased by 10% which, for a Tier 4 Final QSK60 rated at 2850 hp (2125 kW), can mean a fuel burn of 1,100,000 gal (4,200,000 L), depending on duty cycle.
As part of the drive to enhance reliability, our design teams analyzed every possible point on the Tier 4 Final engines that could lead to unscheduled downtime and took measures to prevent it. A good example of this is Cummins new NanoNet filter media. This media, which is used in fuel filters, is designed to ensure superior fuel cleanliness and protect the fuel system from dust or dirt ingress. This enhanced protection is achieved with a more uniform pore size compared to traditional media, so that NanoNet captures and retains more harmful particles.
Like their Tier 2 predecessors, the Tier 4 Final engines are designed with rebuild potential in mind, and are easily capable of three overhauls. Another major benefit is that these engines do not require any major intervention at mid-life. It is likely that few in the industry would have expected that this level of incremental durability and performance for HHP engines would have been compatible with the move to meet Tier 4 Final very low emissions.
Achieving very low emissions
For our Tier 4 Final HHP engines, the focus of PM removal was essentially in-cylinder, which is enabled by multiple fuel injection events using higher pressures. For NOx removal, the focus was moved to the exhaust stream using SCR aftertreatment technology. Removing PM in-cylinder and NOx out-of-engine simplifies the emissions reduction strategy and allows the engine’s full potential to be realized.
Also, without the need to remove NOx in-cylinder, the latitude available within the combustion formula to reduce fuel consumption is broadened significantly. It also allows the engine to operate at higher load factors while staying within a more comfortable range of cylinder pressure and piston speed.
The inherent advantages of SCR aftertreatment are well known across the engine industry. SCR is now the key technology employed for all Tier 4 Final engines in the 75 to 750 hp (56 to 560 kW) category, as well as for every on-highway truck engine in North America. Cummins SCR population in North America has already passed the one million systems mark—a testament to the success of this technology. It is clear that no other approach can offer such significant performance and fuel saving benefits while meeting very low emissions.
Only Cummins has been able to replicate these benefits by migrating SCR technology to HHP engines all the way up to 4400 hp (3280 kW). We design, manufacture, and integrate the SCR system ourselves. We have been able to apply the full range of our expertise with catalyst conversion efficiency, diesel exhaust fluid (DEF) spray pattern injection, and integration control logic to develop our next-generation SCR system uniquely suited for HHP engines.
SCR requires the use of DEF to initiate the chemical reaction over the catalyst. DEF is easy to use, easy to store, widely available, and is also an important means for saving fuel. Fuel savings are improved because using DEF enables Tier 4 engines to employ advanced combustion optimization techniques to improve engine efficiency and reduce tailpipe NOx through the SCR aftertreatment. The resulting optimized product consumes less total fuel and DEF, saving customers roughly 3% on total fluid cost.
In this way, Cummins choice of technology shifts a key cost savings benefit to the operator, as this level of fuel savings is significant for large displacement engines.
Cummins Tier 4 Final engines are designed with the ability to do more, such as move more tons per hour or reach peak torque faster. They have been proven to achieve peak performance under the toughest duty cycles and the highest load factors in the industry. We are sure that no other HHP engines have ever been designed with more inherent strength. We think all of this adds up to a very compelling rationale for our Tier 4 Final approach.
Jim Trueblood, Vice-President, Cummins High Horsepower Engineering, wrote this article for SAE Off-Highway Engineering.
康明斯表示其Tier 4 Final HPP發(fā)動(dòng)機(jī)技術(shù)已達(dá)到并超越該研發(fā)項(xiàng)目的初始目標(biāo)，不僅實(shí)現(xiàn)了4%的燃油節(jié)約，還將大修前使用壽命延長(zhǎng)了10%。圖為康明斯QSK50發(fā)動(dòng)機(jī)。
康明斯高馬力發(fā)動(dòng)機(jī)工程副總裁Jim Trueblood。
康明斯將Tier 4 Final發(fā)動(dòng)機(jī)的生產(chǎn)啟動(dòng)時(shí)間調(diào)整至排放法規(guī)生效日之前，這意味著QSK19、QSK50、QSK60和QSK95等型號(hào)的康明斯發(fā)動(dòng)機(jī)將成為業(yè)內(nèi)第一批上市的Tier 4 Final發(fā)動(dòng)機(jī)。