49915120 林振鋒
The Influence of Compression Ratio on Indicated Emissions and Fuel Economy Responses to
Input Variables for a D.I Diesel Engine Combustion System
柴油引擎燃燒系統中，壓縮比的影響對排放和燃油經濟性的反應。
ABSTRACT
摘要
The effect of compression ratio on sensitivity to changes in start of injection and air fuel ratio has been investigated on
a single cylinder DI diesel engine at fixed low and medium speeds and loads. Compression ratio was set to 17.9:1 or
13.7:1 by using pistons with different bowl sizes. Injection timing and air to fuel ratio were swept around a nominal map
point at which gross IMEP and NOx values were matched for the two compression ratios. It was found that CO, HC and
ISFC were higher at low compression ratio, but the soot/NOx trade-off improved and this could be exploited to reduce
the fuel economy penalty. Sensitivity to inputs is generally similar, but high compression ratio tended to have steeper
response gradients. Reducing compression ratio to 13.7 gave rise to a marked degradation of performance at light load,
producing high CO emissions and a fall in combustion efficiency. This could be eased this by reducing rail pressure, but
the advantage in smoke emission was lost.
壓縮比微量變化的效果，開始噴油空燃比設定為固定值，單缸直噴式柴油引擎低轉速和符合固定。壓
縮比設定為 17.9：1 或 13.7：1 使用不同的活塞大小。噴油的時間和空燃比設定為一個固定值，總的
IMEP 和 NOx 值會適合兩種不同的壓縮比。實驗的結果發現在低壓縮比時 CO，HC 和 ISFC 值會較高，
但碳/NOx 得到了改進，改進的當下可能燃油的消耗將會提升。降低壓縮比之 13.7：1 及給予輕負荷，
CO 的排放增加但燃油的消耗得到改善。
INTRODUCTION
介紹
In recent years, lower compression ratios have been adopted for light duty diesel engines as boost levels have been
raised to increase power densities and reduce part load NOx levels. Designers have long been keenly interested in the
influence of compression ratio (CR) and the optimum value to meet priorities and constraints. In an early investigation,
Yamauchi et al [1] identified 18:1 as giving the highest power output but both higher and lower CR reduced NOx and a
similar early study by Nagai et al. [2] showed that potential routes to reducing NOx included retarding injection timing to
offset the effect of increasing compression ratio. Reduced thermal efficiency from the retarded timing was countered by
the greater expansion ratio. Several theoretical studies have attempted to calculate an optimum compression ratio.
Sood et al. [3, 4] concluded that CR should be 16.4:1 at 1900 rpm, and increase as engine speed deviates from here to
maintain minimum BSFC. A lumped friction and thermal loss term was applied by Bhattacharayya [5], who gives a
comparatively low 15.2:1 as the optimum compression ratio across a variety of cut-off ratios, suggesting that this would
apply for a range of speeds and loads. More recent studies have focused on using the low compression pressures and
temperatures of reduced compression to extend ignition delays, resulting in heavily premixed combustion. In
conjunction with high levels of EGR, low compression ratio can allow extremely advanced injections, resulting in low
temperature combustion of a premixed charge. Ogawa et al. [6] found that EGR>58% had resulted in very low smoke
and NOx, but with a high CO penalty. 14:1 compression ratio extended the load limit of this smokeless NO x-less
combustion to 5.8 bar from only 4.5 bar at 18:1. Difficulties were found with misfire at the highest rates of EGR, and
thermal efficiency was reduced even with optimum timing. Similar results were found by Beatrice et al. [7] on reducing
the compression ratio of a production engine from 16.5:1 to 14.5:1. High rates of EGR at LCR gave no smoke penalty
over conventional combustion, although conventional combustion had a 5% ISFC penalty due to poor combustion
and thermal efficiency at lower loads. Early injection at low and medium load resulted in ultra-low soot and NOx, but
high load operation was not possible due to noise limitations. The downside was CO and HC penalties in the order of
200%, plus a 10% increase in fuel consumption.
近年來，採用了壓縮比低的輕型柴油引擎提升水平提出了提高功率密度，降低部分負荷段的 NOx 排
放。在早期的調查中，Yamauchi(1)發現單孔直噴給予 18.1：1 的空燃比可以得到最高功率但(CR)的變
化忽高忽低，減少 NOx 的排放。(2)的報告表明了潛在的因素，要減少 NOx 的排放延遲點火時間及提
高壓縮比也有一定的影響。經過多年的研究幾乎都想計算出最佳的壓縮比。(3)(4)認為，壓縮比在 16.4：
1 在 1900 轉，會提升引擎的性能並達到最低的油耗。彙整了所有抹茶和人損失的數據，長期應用在(5)，
得到一個最佳的壓縮比為 15.2：1 適合在各種環境下，這表明適合用於各種速度和負載。最近的實驗
多數集中在低壓縮壓力及把溫度降低延遲點火時間，結果發現導致嚴重的預混燃燒。結合廢棄在循環
（EGR）
，在低壓縮比可以使用高壓噴嘴結果達到低溫預混和燃燒。Ogawa(6)實驗發現，EGR>58%會產
生低的黑煙排放和 NOx 排放，但代價是 CO 的排放增加。壓縮比從 14.1：1，加大負載限制無煙 NOx-less
燃燒在 5.8bar 只有 4.5bar 在 18.1：1 的壓縮比。實驗中發現在引擎點火失效時廢氣排放最嚴重及熱效
率大大減低。類似的實驗結果在 Beatrice(7)引擎在設計是設法降低壓縮比，最好保持在 16.5：1 或 14.5：
1 的。早期的噴射，在低中負荷會產生低煙塵低 NOx 排放，但高負荷情況就會惡化由於噪音的限制。
導致 CO 和 HC 的排放增加，加上提高 10%燃油消耗。
Bression et al. [8] found lower PM at low CR could be used to offset the effect of reduced swirl ratio and avoid a PM
penalty whilst improving fuel consumption. 15:1 gave optimum results compared to both 16 and 14:1. Using a split
main injection helped fuel consumption while reducing HC emissions but PM increased due to the second part of the
main burning in a diffusion flame. High levels of EGR were also used by Li et al. [9], who found CO emissions went up
with EGR, but smokeless operation was achievable at all compression ratios, even when injecting into a combusting
charge, suggesting that soot production was avoided with low temperatures, not high mixing. The combination of low
compression ratio, high EGR and fuel with reduced Cetane number allowed ignition delays to be extended at loads as
high as 6.5 bar and although there was a thermal efficiency penalty much of this was compensated for by lower heat
rejection to coolant. Computational modelling [6, 9, 10] and experimental data have illuminated the way in which low
CR value affects the soot NOx trade-off on the Φ-T map. The conclusions suggest that the extended mixing and lower
temperatures of low CR enable combustion to both miss the soot formation peninsula and avoid significant penetration
into the high temperature NOx zone. However, KIVA combustion modelling by Murata [10] on a low effective
compression ratio engine revealed that significant liquid fuel could be deposited on the bowl walls, increasing CO
emissions.
Bression(8)發現低 PM 在低 CR 作用可以用來抵消渦流（漩渦）比帶來的影響和避免 PM 影響了燃油的
消耗。15.1：1 與 16：1 和 14.1：1 相比，利用分裂方式主要幫助燃燒消耗同時降低 HC 的排放，但
PM 增加，主要由於第二部分主要燃燒，擴散火焰。LI(9)理由 EGR 研究，發現 EGR 作用會提升 CO 的
排放，但無黑煙的操作可以實驗在所有的壓縮比。這是表明煙塵的生產是避免氣溫低得不到高的混和
比。相結合的低壓縮比，高 EGR 和降低燃油辛烷值可以延遲點火時間，加大負荷最高可到達 6.5bar，
雖然有熱效率的損失需要使用散熱冷卻來進行補充。計算模型(6.9.10)和實驗的數據對照，低 CR 值影
響了 NOx 平衡的地圖。結果表明，混合比的改善，和低溫低 CR 燃燒的效果不好。然而，KIVA 燃燒模
式 Murata(10)在低壓縮比的引擎上，燃料可以存放在碗壁，增加 CO 的排放量。
Lagguiton et al. [11] found that low compression did not affect NOx at light loads, where combustion was premixed.
At high loads, retarding injection timing increased premixed combustion when timings were advanced from TDC and
ignition delay was increased, resulting in partially premixed combustion at both ratios. It was concluded that NO x
production in premixed mode is not dependant on temperatures and pressures, but that NOx development in
diffusion combustion is. Ogawa et al.[12] considered step changes in load with a single cycle emissions sampling
technique. Steady state HC emissions were doubled when CR was reduced from 19:1 to 16:1, and trebled again when
CR was reduced to 13:1. A step increase in load led to an increase in HCs of more than 5 times within ten cycles,
taking around 1000 more cycles to level off. The increase in emissions was exacerbated by reducing coolant
temperature from 80°C to 15°C and 13:1 was much more significantly affected than the other compression ratios. The
current study of performance at two compression ratios is restricted to conventional combustion regimes with EGR <
20%. Comparisons are made of engine performance at a relatively high (17.9:1) and relatively low (13.7:1)
compression ratio when performing a simple swing in inputs of SOI and AFR. It attempts to ensure that all other
parameters are held constant to give the best possible chance of interpreting the results with further analyses such as
heat release and combustion stability.
Lagguiton(11)發現，在輕負荷時低壓縮不影響 NOx 的排放，在幫助預混燃燒。在高負荷時，延遲噴油
時間增加預混和燃燒的時間，時間和點火延期的增加，導致部分預混燃燒比率。實驗的結論是，在預
混和的過程中產生 NOx 的，預混模式不依賴溫度與壓力。Ogawa(12)認為一步步改變負荷的變化以一
個週期的排放順序觀察採取技術。在穩定的狀態下 HC 排放增加一倍，當 CR 減少時是 19.1 到 16.1 之
間，當 CR 再次減少以達到 13.1。一個步驟增加負荷導致增加 HC 的排放 5 倍以上在十個週期內，取
的數據是在 1000 個週期達到平衡。排放增加加劇了冷卻的效果 80 度至 15 度在 13.1，更是顯示這樣
的效能影響了其他的壓縮比效能。目前的研究表現兩個不同的壓縮比在得到常規燃燒制度的限制與
EGR<20%內。比較了引擎兩個不懂條件的性能，一個是相對較高的 17.9:1 和較低的 13.7:1 壓縮比，當
執行一個簡單的實驗輸入 SOI 和 AFR 確保所有其他參數保持不變，再進一步分析，實驗熱釋放以及燃
燒的穩定性。
EXPERIMENTAL FACILTIES AND TEST METHODOLOGY
實驗設備和測試方法
The test engine was a Ricardo Hydra, 550 cc single cylinder engine with a Ford DI combustion system. In production
form the combustion system allows Euro IV emissions regulations to be met with a CR of 15.5. The fuel injection
equipment comprised an 1800 bar HPCR system with 7-hole solenoid injectors. The test engine had a horizontally split
block which allowed the upper part and head to be raised. This made changing the piston relatively easy; it avoided
disturbing the crankshaft encoder and minimized build to build variation. Geometric compression ratio values of
13.69:1 and 17.91:1 were set using pistons with different bowl volumes. The bowl shape was maintained as the
original. These will be referred to as Low and High Compression Ratios (LCR and HCR for brevity),
respectively. HCR is typical of the compression ratios used throughout the Euro IV period; the LCR value is below any
value used in current production and close to the limit of diesel engine operation. In both cases the bowl shape was the
same as in the production piston.
利用 Ricardo Hydra 作為人體測試，550cc 的 FORD 單缸引擎直接噴射系統。在生產的形式燃燒系統允
許歐洲 IV 排放法規達到 DR 值 15.5.燃料設備包括 1800bar HCPR 系統，7 孔的電磁噴油嘴。測試引擎
有一個水平的分塊，使上部和頭部被提出。這使得改變活塞的工作相對容易，它避免了曲折編碼器和
最小化建立建設改變。幾何壓縮值為 13.69:1 及 17.91:1 設置使用活塞碗量不同。碗的形狀保持原來
的不變。這些被稱為低壓縮比和高壓縮比的比率分別。HCR 類型的壓縮比使用 LCR 種類，低於任何一
種目前生產的引擎，是柴油引擎中的極限。這兩種情況下的碗形狀是一樣的生產活塞。
The engine intake air was boosted by an external supply of compressed air. A 100 litre pressure vessel in the supply
line was used to damp pressure fluctuations. Exhaust backpressure was controlled using a stepper-motor-controlled
butterfly valve downstream of the exhaust manifold and EGR port. The intake pressure regulator and backpressure
stepper motor were controlled through a National Instruments data acquisition system to achieve target pressures.
K-type thermocouples were used for temperature measurements and allowed oil, coolant, and intake air temperatures
to be controlled with auxiliary heaters. Fuel delivered to the HPCR was cooled to 20°C. Fuel consumed by the engine
was measured using a positive displacement flow meter.
引擎的進氣系統吸入的空氣是由外掛空壓機所提供的壓縮空氣。排氣背壓控制使用步進馬達控制蝴蝶
閥下游的排氣歧管和EGR端口。進氣壓力調節器和背壓的步進馬達控制所有通過儀器的數據，採集系
統實現我們所需的壓力。K-type的熱電偶（thermocouples）進行溫度測量，以及允許有，冷卻液，
進氣溫度進行控制補助加熱器。燃料輸送到HPCR冷卻到20度，燃油的消耗性使用位置移流量計作為量
測。
A Horiba MEXA-7100 DEGR exhaust gas analyzer system measured engine-out emissions, whilst an AVL 415 smoke
meter provided smoke measurements. AFR was calculated from an oxygen balance using the measured exhaust gas
composition as defined by Heywood [13]. Cylinder pressure was measured using a Kistler 6125 piezoelectric pressure
transducer and Kistler 5011 charge amplifier. Pressure data triggered by the 2500 ppr shaft encoder were recorded
against crank angle and ensemble-averaged over 50 cycles. Net heat release was determined by First Law analysis as
defined by:
(1)
For each compression ratio, performance was investigated around two set points. The first was at a speed of 2000 rpm
and a load of ∼11 bar IMEPg. This is representative of a high speed cruise in top gear or part of an acceleration
transient. Baseline calibration values of fuelling, boost and backpressure were matched to the production calibration
settings. Single-factor sweeps of SOI (+/−5°) and AFR (+/−1) were conducted around these baseline points. The
IMEPg and NOx results found at baseline settings for HCR at the centre point for the sweeps were reproduced at the
LCR through small adjustments to the fuelling and/or AFR. Generally, 4 repeats were performed to enable some
characterisation of test to test repeatability and 95% confidence limits to be applied. The investigation was repeated at
the second set point, which was a speed of 1500 rpm and a load of 3 bar IMEPg. This is representative of low speed
urban driving conditions.
使用 Horiba MEXA-7100 作為我們的尾氣分析儀系統，測量發動機的排氣量，AFR 是計算排氣成分的
含氧量以界定 Heywood。氣缸壓力使用 Kistler 6125 壓電式壓力感測器，和 KIstler5011 電荷放大
器。壓力數據使用 2500ppr 曲軸編碼器記錄曲折轉角和以平均超過 50 週期來進行分析。
熱釋放由第一定律分析的定義：
每个压缩比，性能进行了 2 组分。第一次是在 2000 转的速度和负载的∼11 杆 imepg。这是代表一个
高速巡航在最好的部分或加速度瞬变。基线校准值加油，鼓舞和背压匹配生产校准设置。单扫描技术
（+/−5°）和非洲（+ /−1）进行了围绕这些基准点。imepg 和氮氧化物的结果发现在基线设置热送热
装在中心点的彩票被复制的比率通过小调整到加油和/或空燃比。一般来说，4 个重复进行，使一些特
性的测试，测试的重复性和 95%置信限被应用。调查是在重复二点，这是 1500 转的速度和负载的 3
杆 imepg。这代表的是低转速的城市驾驶条件。
49915122 陳維翰
SOI 開始注射
Results of the SOI and AFR sweeps at the high load point (2000 rpm, 11 bar) are plotted in Figure 1 and Figure 2 for
the two compression ratios. Pilot fuel delivery was 1.5 mm3/str with fixed separation. The main injection quantity was
increased to achieve the same IMEPg at low compression ratio and NOx matched by adjusting EGR valve position and
hence AFR at the set point. The data for sweeps of injection timing about the centre point are presented in Figure 1.
The sensitivity of IMEPg to the timing of the start of injection (SOI) is independent of compression ratio and the results
virtually overlay. Several dependent variables are higher for the LCR case with an almost constant increase above the
HCR results across the range of SOI covered. These are fuel, gross ISFC, gross ISHC, and gross ISCO. Values of
AFR and EGR were lower with again constant offset. Smoke FSN numbers were lower for the LCR case, and notably
less sensitive to SOI than for the HCR case. The data for sweeps of AFR are presented in Figure 2. Fuel flow, gross
ISFC, gross ISHC and gross ISCO were higher for the
LCR case as before, and exhibited the same sensitivity to AFR; EGR levels were slightly lower and showed the same
sensitivity to AFR and NOx results overlaid. Smoke FSN numbers were relatively low for the LCR results and similarly
less sensitive to changes in AFR as SOI.
SOI 和 AFR 的掃描結果於高負荷點(2000rpm,11bar)繪製在圖 1 和圖 2 的兩個壓縮比率。試點燃油輸
送 1.5mm3/str 與固定的分隔。主噴射量的增加，在低壓縮比和 NOx 的匹配通過調節 EGR 閥來達到同
樣的 IMEPg 位置和因此 AFR 在設置點。噴油正時關於中心點的掃描數據顯示於圖一。IMEPg 的靈敏度
到時序的開始注射（SOI）的是獨立的壓縮比,結果幾乎重疊。多個因變量是高於 LCR 的情況具有幾乎
恒定的增加以上的 HCR 結果跨越 SOI 所涵蓋的範圍。ISFC 總值，ISHC 總值，和 ISCO 總值,這些燃料。
AFR 和 EGR 的值較低再次恒定的抵消。在 LCR 的情況下,FSN 的煙氣分別爲較低的,尤其是在 HCR 的情
況下較不靈敏的 SOI。 AFR 的掃描數據呈現出在圖二中。ISFC 總值,ISHC 總值和 ISCO 總值的燃料流
量為較高在 LCR 的情況前,並表現出相同的靈敏度 AFR;EGR 水平顯得略低，顯示了相同的靈敏度 AFR
與 NOx 的結果重疊。LCR 的結果 FSN 的煙氣數量相對較低和類似的變化較不靈敏在 AFR 當於 SOI 時。
The rates of heat release for the low and high compression ratio cases at the midpoint are shown in Figure 3. For the
LCR case, combustion of the pilot and the main occur around
4°CA later and the premix combustion spike is twice the HCR value. The greater degree of premixing reduces soot
production and as indicated by Figure 4, bulk gas temperature
is higher during the power stroke, despite being lower at the end of compression. This and the lower sensitivity to
retarded SOI timings indicate the oxidation of soot is more efficient.
In the round, the reduction in compression ratio improves the soot-NOx trade off, as shown in Figure 5, at the expense
of an increase in gross ISFC, ISHC and ISCO.
熱釋放效率的低與高壓縮比的中點處顯示於圖三。LCR 的情況下，燃燒的試點主要發生在 4°CA 後及
預混合燃燒是 HCR 值的兩倍。最大程度的預混合會減少油煙的生產，如圖四所示，總體氣體的溫度會
較高在動力衝程的期間，儘管為較低的在壓縮結束時。較低的靈敏度延遲 SOI 時序,顯得所氧化的油
煙更高效率。壓縮比的減少改善了油煙 NOx 的平衡，如在圖五中所示，以犧牲有所增加 ISFC 總值,ISHC
總值和 ISCO 總值。
The midpoint ISFC for high compression ratio, as shown in Figure 1 and Figure 2, was 202g/kWh. Dropping to the
lower compression ratio raised ISFC to 211g/kWh at the midpoint.
By taking advantage of the reduced sensitivity of soot to SOI with lower compression, the fuel economy penalty of the
low compression ratio could be reduced to some extent by advancing injection timing and the effect on NOx contained
by increasing EGR. Advancing SOI an extra 8° and increasing EGR from 4.6% to 8.6% improved gross ISFC of LCR
from 211 to 206g/kWh without a significant NOx penalty over the HCR case and still maintaining soot levels
approximately half that of HCR. However this came at the cost of a large increase in peak dP/dθ and a high level of
noise which was deemed likely to be unacceptable.
ISFC 中間點為高壓縮比，如在圖 1 和圖 2 所示，為 202g/kWh。下降至較低的壓縮比籌集 ISFC 至
211g/kWh 在中間點。通過利用靈敏度降低油煙 SOI 在較低的壓縮時，燃料經濟性的損失可能會減小
到一定的程度，由促進的噴射正時及對 NOx 的效應包含通過增大 EGR。推進 SOI 一個額外的 8°及增加
EGR 從 4.6％至 8.6％改善了 ISFC 總值於 LCR 從 211 到 206g/kWh 無需一個顯著的 NOx 損失過度 HCR
的情況，仍保持 HCR 的油煙水平約一半。然而，在峰值 DP /dθ時帶來大量增加的成本和高的噪音水
平，這被認為是不可接受的。
A summary of sweep results for the second set point, 1500rev/min and an IMEPg of 3 bar, is presented in Figure 10
and Figure 7. At the midpoint, ISNOx was matched for the LCR and HCR cases; the AFR at the set point was raised
from 38:1 for the HCR to 45:1 for the LCR tests, producing a reduction in EGR from 18% to 9%, to allow injection timing
to be swept to retarded values without combustion deteriorating dramatically. However, the responses for
sweeps of SOI given in Figure 6 show that even with reduced EGR levels and much greater air availability at LCR,
gross ISHC and ISCO values are an order of magnitude higher than values at the first set point and values at LCR are
typically four times higher than the corresponding HCR value. What was an ISFC penalty of a few percent at the first
set point widened to ∼20% with more potential for variability at 1500rev/min, 3bar IMEPg. The increased AFR enabled
LCR to be relatively insensitive to changes in AFR, but this was not the case for injection timing, where any retard from
baseline produced a rapid reduction in work ouptut and large
increases in CO and HC not seen at HCR. Advancing and leaning could not rectify the situation suggesting that this is a
physical limit under these conditions at LCR.
掃描結果的摘要 1500rev/min 和一個 IMEPg3bar 在第二設定點，呈現在圖十和圖七中。在中點，ISNOx
於 LCR 與 HCR 的情況下是匹配的; AFR 在設定點籌集從 38:1 為 HCR 上升至 45:1 於 LCR 測試，使得
EGR 減少從 18％至 9％，允許噴油正時被掃描滯後值未經燃燒大量惡化。然而， SOI 掃描的反應在圖
6 中顯示，即使降低 EGR 水平和更多的空氣可用性在 LCR， ISHC 總值和 ISCO 值是一個大數目的，高
於第一點的值及 LCR 值通常相應 HCR 值高出四倍。ISFC 損失的百分比於第一設定點擴大至〜20％與
更多的潛在的可變性在 1500rev/min, 3BAR IMEPg。增加 AFR 使 LCR 在 AFR 的變化相對不靈敏，但是，
這不在噴油正時的情況下，任何滯留，從基線產生迅速減少工作中的輸出及觀察不到在 HCR 中 CO 和
HC 的大量增加。進展和學習，不能糾正的情況，建議這是一個物理極限,在這些條件下於 LCR。
圖一：HCR 與 LCR 噴射正時總結反應的掃描於 2000rpm 高負載時，平均結果與 95%信賴限度。
圖二：HCR 與 LCR 空燃比總結反應的掃描於 2000rpm 高負載時，平均結果與 95%信賴限度。
圖三：壓縮比於中間點高負載的情況下熱釋放的效應。
圖四：壓縮比於中間點高負載的情況下總體氣體溫度的效應。
圖五：SOI 油煙/NOx 權衡掃描從滯留至提前的時序於三種壓縮比，13.7:1（完整的圓），15.5:1（空
心圓）和 17.9:1（空心方塊）
圖六：HCR 與 LCR 噴射正時總結反應的掃描於 1500rpm 低負載時，平均結果與 95%信賴限度。
圖七：HCR 與 LCR 空燃比總結反應的掃描於 1500rpm 低負載時，平均結果與 95%信賴限度。
圖十:LCR 於 1750rpm 低負載時的共軌壓力的掃描總結反應，平均結果與 95%信賴限度。
49915008 葉詠碩
The effect of changing SOI on combustion stability,efficiency and thermal efficiency corrected for the
amount of fuel which was combusted in each case is shown in Figure 8.Advancing SOI offers little gain
whilst retarding SOI produces a rapid deterioration in all three in the LCR case. Thermal effects account for
the majority of the ∼4% ISFC penalty when moving from HCR to LCR at high load. At low load, there is a
further increase in ISFC due mainly to a ∼3% reduction in combustion efficiency and a five-fold increase in
CO and HC emissions.
在圖 8 中示出的效果改變 SOI 燃燒穩定性，效率和熱效率為在每種情況下被燃燒的燃料的量校正。上
升的 SOI 提供了較少的增益，在所有三個 LCR 的情況下，而延緩 SOI 生產的迅速惡化。從 HCR 轉移
到 LCR 在高負荷時大多數熱影響占油耗的 ∼4%。在低負荷時，油耗進一步增加主要是由於燃燒效率
減少了 ∼3%且 CO 和 HC 排放量增長了 5 倍。
Fuel penetration is inversely related to cylinder pressure and several studies [14, 15, 16] indicate that diesel
sprays reach the piston bowl wall within the ∼1 ms ignition delay period. At low compression ratio, low
load, the ignition delay of the main is extended by ∼13% from the high compression case, and cylinder
pressure at time of injection is ∼15 bar lower than the 52 bar seen at HCR. This suggests that significantly
more fuel will wet the bowl surface, accounting for the increase in HC. It also appears likely that the
extended ignition delay and penetration produces the large reduction in smoke levels seen across the
board at LCR due to the longer time and greater penetration afforded by the lower pressures and
temperatures. These increase entrainment and reduce local equivalence ratios so that the soot peninsula
of the Φ-T map is avoided.
[14，15，16] 的一些研究表，說明在 ∼1 ms 點火延遲期內柴油噴霧劑達到活塞碗牆和燃油滲透成
反比有關的氣缸壓力。低壓縮比，在低負荷下，點火延遲從最高壓縮的情況下擴展約 ∼13%，和在噴
射時的氣缸壓力 15bar 低於 HCR 的 52 bar。這表明，更多顯著的燃料弄濕缸體的表面，造成 HC 的增
加。這似乎也可能延長點火延遲和滲透全線由於時間較長，在 LCR 產生的煙霧濃度大量減少和較低的
壓力和溫度下所能提供的更大的滲透。這些增加夾帶和 Φ-T 地圖的煙塵半島是避免減少本地等價的
比率。
Figure 8. HCR vs LCR low load IMEPg stability, combustion efficiency and thermal efficiency of combusted fuel for a sweep
of injection timing.
Considering the high load case, where combustion efficiency is similar for both LCR and HCR cases, we still
see an extension of ignition delay and would expect greater penetration. The rapid combustion of the large
main increases bulk temperatures in the low compression case to those seen at high compression. This
implies soot formation is lower at LCR, but that the rates of soot oxidation would be comparable, hence the
significant reduction in engine out FSN. With high fuelling, bulk temperature calculated with PVn reaches
1550K vs. only HOOK at low fuelling. This likely explains the reduction in combustion efficiency; with lower
bulk temperature it will be less likely that fuel around the cooler piston walls will fully combust, hence the
large increase in CO and HC. This is especially likely at retarded injection timings, where temperatures and
pressures are reduced substantially.
考慮到在高負荷的情況下，燃燒效率是相似的 LCR(低壓縮比)和 HCR(高壓縮比)情況下，我們仍然可以
看到點火延遲的延伸，期望更大的滲透。低壓縮和高壓縮相比，在這情況下快速燃燒的最主要是增加
體積溫度。這意味著在 LCR 煙塵形成較低，但碳煙氧化率相當完美，使引擎排出 FSN 顯著減少。在
高入油量，由計算體積溫度與 PVn 達到 1550K 與唯一的鉤在低入油量。這可能解釋了燃燒效率的降
低；與體積溫度較低，它將活塞壁周圍較冷的燃料不太可能充分燃燒，因此使 CO 和 HC 的大量增
加。這是特別有可能在延遲噴射定時改善，特別是溫度和壓力被大幅降低與減少。
Optical studies [17,18] indicate that temperatures in the region of 1200K and 1500K must be reached for
complete combustion of HC and CO, respectively, indicating the
difficulties faced at LCR. Figure 9 shows the relationship between calculated peak bulk gas combustion
temperature and measured combustion efficiency at low load. Combustion efficiencies level off at around
99% and 97% at the most advanced timings for the HCR and LCR cases, respectively. The LCR combustion
efficiency was not raised by increasing the AFR by 5 points, suggesting that reduced compression pressures
and temperatures of LCR were allowing excessive spray penetration and wall wetting at the low load. In
principle, the over-penetration can be limited by reducing fuel rail pressure and to explore this, a rail
pressure study was performed at the low load for LCR only. Rail pressure was varied from the baseline
∼580 bar in steps of 100 barbetween 280 and 680 bar. AFR and SOI were set at the standard calibration
midpoints.
光學研究[17,18]表示，在溫度 1200K 和 1500K 的地區必須達到完整的燃燒的 HC 和 CO，分別表示 LCR
所面臨的困難。圖 9 顯示出計算峰值之間的大宗氣體燃燒溫度和測量在低負荷時的燃燒效率兩者間的
關係。燃燒效率水平在大約 99％和 97％，分別在最先進的 HCR 和 LCR 的案件。LCR 並沒有增加燃燒
效率且提昇 AFR 到 5 個百分點，表明了減少的壓縮壓力和溫度的 LCR，在低負荷允許過度噴霧滲透缸
壁潤滑。在原則上，過度滲透可透過限流來減少燃料軌壓力和並探討，共軌壓力的研究，僅在低負荷
LCR 執行。管路壓力是從基線 ∼580 bar 間變化，其中 100 bar、280 和 680 bar 的步驟各不相同。AFR
(空燃比)和 SOI 決定標準校準點位置。
Figure 9. HCR vs LCR low load IMEPg(平均有效壓力) combustion efficiency compared to calculated maximum in cylinder
temperature.
Reducing rail pressure required longer injection duration to inject the same amount of fuel. Demanded
injection quantity was adjusted to keep fuel flow constant at ∼0.5 kg/hr and injection was advanced with
reducing rail pressure until calculated thermal efficiency was constant at ∼37% to minimise effects other
than those due to changes in rail pressure. The largest difference in piston height due to different injection
timings was 1.7 mm for the pilot injection, where only 1.5 mm3 of fuel is called for. The main injection
event, where the majority of fuel is injected, starts earlier at low rail pressure but since piston motion is
small around TDC, this resulted in a maximum piston height difference of only 0.12 mm. Longer injection
duration at low rail ressure ensured end of injection was similar for all tests, so any wall wetting effects
would be entirely due to changes in spray penetration, not geometric differences. The main effect of
reducing rail pressure on net heat release characteristics was to reduce the peak value from 50 to 36J/°CA
as rail pressure was reduced from 680bar to 280bar. Ignition delay was constant and the advance of SOI
with reducing rail pressure maintained an almost constant crank angle location of peak heat release. A
summary of results is presented in Figure 10, along with the effects of rail pressure on combustion
stability and efficiency for the set thermal efficiency in Figure 11. Both CO and HC reduced by just over 30%,
increasing combustion efficiency by 1% to 97.5%, when reducing rail pressure from 680 bar to 280 bar. Even
the lowest rail pressure did not compensate for the reduction in compression ratio, however. CO and HC
remained 2-3 times higher than the HCR results, and the poor atomisation and lower penetration lead to
locally rich regions, resulting in similar smoke emissions to HCR. While chamber pressure has a stronger
impact on spray penetration than injection pressure [14, 19], it is unlikely that differing spray penetration
alone is the reason for poor combustion efficiency at low load, low compression ratio; rather this is due to a
combination of overpenetration and low temperature.
減少油管壓力後，需要注入相同量的燃料噴射持續時間更長。要求的噴射量的調整，以保持燃料流量
恆定在〜0.5 千克/小時和噴射提前與減少油管壓力，直到計算出的熱效率與減少的時間是恆定在〜37
％，以減少那些由於油管壓力的變化以外的效果。最大的區別在活塞的高度，由於不同的噴射定時為
先導噴射，其中只有 1.5 立方毫米的燃料被稱為為 1.7 毫米。主噴射的事件，其中大部分的燃料注入，
早些時候開始在油管壓力低，但由於活塞運動是小範圍 TDC(上死點)，這導致了一個最大的活塞的高
度差僅為 0.12 毫米。在保證注射結束的低鐵法蘭壓力注射時間長是類似的所有測試，所以任何牆面
潤濕效果會完全是由於在噴霧滲透的變化，不是幾何的差異。油管壓力從 680bar 降低至 280bar，減
少淨放熱特性上油管壓力的主要作用是減少高峰值從 50 到 36J/°CA。點火延遲是恆定的，增加的 SOI(開
始噴射時間) 俱進減少油管壓力保持幾乎恒定的曲軸角位置的峰值熱釋放。結果摘要提出在圖 10 中，
在圖 11 中所設置的熱效率中的燃燒穩定性和效率上對管壓的影響。油管壓力從 680 bar 減少到 280
bar，CO 和 HC 超過 30％並增加燃燒效率 1%至 97.5%。即使是最低的軌壓力沒有補償的壓縮比降低。
然而 CO 和 HC 仍然高於 HCR 結果 2-3 倍，和差霧化和低滲透本地豐富的地區，導致向 HCR 排放
類似黑煙。雖然室壓力噴霧穿透比噴射壓力[14，19]具有較強的影響，在低負荷不可能單獨變化不同
的噴霧穿透，低壓縮比的燃燒效率差的原因，而這是由於過度穿透和低溫度的組合。
Figure 10. Summary responses for a sweep of rail pressure. 1750 rpm, low load, LCR. Averaged results with 95% confidence
limits.
Figure 11. LCR low load IMEPg stability, combustion efficiency and thermal efficiency of combusted fuel for a sweep of rail
pressure.
49915047 陳俊宇
CONCLUSIONS
結尾
The effects of sweeps of injection timing and AFR on various engine output parameters have been studied at two
compression ratios. Reducing the compression ratio led to increased ISFC at both a low and high load condition. At
high load, the effect was small, and could be partially offset by exploiting a much improved soot-NOx tradeoff and
reduced NOx with advancing SOI. In practice a steep increase in audible noise limits the advance which can be used
and the ISFC improvement that can be achieved. LCR gave large soot production benefits over HCR at all conditions
tested, implying that it may be a route to reduced dependency on diesel particulate filters for tightening emissions
legislation compliance.
射入時間和 AFR 打掃的作用對各種各樣的引擎輸出參數被學習了在兩壓縮比。減少壓縮比導致了增
加的 ISFC 在一種低和高負荷狀態。在高負荷，作用是小的並且能通過剝削被改進的煤灰氮化物交易
和減少的氮化物部份地抵銷以推進 SOI。實際上可聽得見的噪音限度的急增限制能被使用的和可以達
到的 ISFC 改善。LCR 在所有的測試情況提供在 HCR 上的大煤煙生產利益，它在柴油屬於顆粒的過
濾器也許是路線到減少的附庸為加強放射立法服從。
A low load study revealed severe degradation of combustion efficiency at LCR not seen at HCR, evidenced by large
increases in CO and HC. It was necessary to lean the mixture out significantly at LCR to allow any comparisons to be
made. Combustion temperatures were too low for thorough oxidation of CO or HC, likely exacerbated by increased
spray penetration and greater wall wetting at LCR. This has a knock-on effect in real world applications as low
combustion temperatures generate high emissions of unburnts, which cannot be oxidised by the exhaust catalyst due
to the low engine-out temperature. Some improvement in low compression ratio combustion efficiency was found by
significantly reducing rail pressure. Lower spray penetration likely reduced the total amount of fuel deposited on the
bowl wall, but the effect was reduced by poor rates of heat release and lower peak temperatures. Only around 1/3 of
the improvement required to meet HCR emissions of CO and HC was achieved, and this was while sacrificing the LCR
soot benefit.
一項低的負荷研究在 HCR，因 CO 和 HC 的增加而不被見到的 LCR 的燃燒效率的嚴格降格。在
LCR 重要地在外倚靠混合讓任何的比較被做是必需的。燃燒溫度過低徹底氧化的 CO，HC，增加噴
霧的滲透和更大的壁浸潤在 LCR 可能加劇。當低的燃燒溫度產生高排放物時，這在真正的世界申請
中有漏球結果不燃燒，由於低的引擎，這不能夠被排氣催化劑使氧化－外面的溫度。在低壓縮比燃燒
效率的一些改善是通過重大減少路軌壓力發現的。下部噴射滲透率可能降低燃料的總量沉積在碗壁，
但這樣的效果是減少了較差的熱釋放率和較低的峰值溫度。只有約 1/3 以滿足 HCR 的 CO 和 HC 的排
放量所需要的改善實現，而且當犧牲 LCR 煤煙時這是有益。
While some improvements in emissions of NOx and soot may be achieved with a reduction in compression ratio, this is
generally paid for by a reduction in thermal efficiency and an increase in emissions of HC and CO. This may be
tolerable at higher loads, but is a cause for concern at low loads and a limiting factor on the lowest value of
compression ratio that might be used. Although a compression ratio of 13.7:1 offers some benefits for high load
operation, the deterioration in performance at light load is a serious impediment to its adoption for operation at fixed
compression ratio.
雖然一些改善排放的 NOx 和煙灰實現與壓縮比的降低，這為對熱效率的減少和在 HC 和 CO 放射的增
量通常是有償的。在較高的負載，這是可以容忍的，但在低負荷時的關注和壓縮比的最低值時可能會
用到的一個限制因素。雖然壓縮比為 13.7:1 的高負荷運行提供了一些好處，在輕負載時的性能下降，
嚴重阻礙其通過工作在固定的壓縮比。