（1）噴射延遲階段

噴油器向氣缸噴油的時(shí)刻比油泵內(nèi)壓力開(kāi)始上升的時(shí)刻要落后一段時(shí)間。造成這種現(xiàn)象的主要原因，首先是由于出油閥上的卸荷容積作用，當(dāng)油泵壓力開(kāi)始上升時(shí)，必須等到卸荷容積與高壓油管相同后，燃油方能進(jìn)入高壓油管；其次，是在高壓下因燃燒和高壓油管的彈性作用，燃油被壓縮而高壓油管內(nèi)的容積增大，故壓力上升較緩慢。

所以在噴油泵供油開(kāi)始后，高壓系統(tǒng)中的油壓升高，直到噴油器內(nèi)壓力升到針閥的啟閥壓力時(shí)，針閥才能開(kāi)啟上升，使燃油噴入汽缸。

   （2）主要噴射階段

噴油器內(nèi)的壓力較高，大部分燃油在此階段噴入汽缸，而且是在不斷增高的壓力下噴入的，其霧化效果比較理想。次階段取決于柴油機(jī)的負(fù)荷，負(fù)荷越大，此階段越長(zhǎng)。

   （3）滴漏階段

在這階段中，噴油器的壓力從最高噴油壓力一直下降到針閥的落座壓力。

3、噴油規(guī)律及其要求

Fuel injection and combustion system for diesel generator engine
First, diesel engine fuel injection
1, the composition of the fuel injection system
Role of the fuel injection system, is at a very high pressure at a certain moment will quickly a certain number of fuel injected into the cylinder, make it spray. Injection system is composed of the main device is fuel injection pumps, injectors and high-pressure tubing.
2, injection process
Characteristics of injection process can be divided into Jet delayed, spray and drip three main stages.
(1) blast delayed phase
Fuel injector cylinder pressure began to rise within the moment of injection pump always lagged behind those for some time. Caused this phenomenon of main causes, first is due to out valve Shang of unloading Dutch volume role, dang pump pressure began rose Shi, must until unloading Dutch volume and high pressure tubing same Hou, fuel party can entered high pressure tubing; second, is in high pressure Xia due to combustion and high pressure tubing of elastic role, fuel was compression and high pressure tubing within of volume increases, so pressure rose more slow.
So after the start of injection pump oil, hydraulic high pressure system rises, until the needle valve of injector pressure rise when Kai valve, needle valve can be opened up, fuel injected into the cylinder.
(2) the main injection phase
Higher pressure in the injector, and most of the fuel injected into the cylinders at this stage, but is under pressure from the rising spray into, ideally its fog effects. Second phase depending on the load of diesel engine, large loads this phase longer.
(3) the dripping phase
In this phase, the injector pressure maximum injection pressure has been down to needle valve seat pressure.
3, injection and its requirements
(1) fuel injection rate
The so-called injection, is a cyclic injection quantity distribution throughout the injection duration, that is, each ' participation in distribution curve of the handle angle spray oil.
(2) injection delays
Fuel injection delay was mainly due to fuel can be compressed, high pressure oil pipe caused by fluctuation phenomena in elastic and high pressure tubing.
4, the factors affecting fuel injection rate
(1) cam curve and effective work
Fuel pump cam determines the plunger motion law, and rapid variation of the plunger pump decision for law, thus affecting the injection. Effectively in the piston stroke and starting point for oil under the same circumstances, cam shape more steep, oil rise faster, larger oil supply speed, fuel injection delays and injection angles the smaller.
(2) the piston diameter and orifice diameter
Without changing the piston stroke increases when the piston diameter, speed increases for oil, fuel injection delays and continuous angles are reduced, in favour of combustion in the previous check point near the end, diesel economy getting better. But the initial injection rate to increase, will participate in the burning oil increased when the fire started, running rough.
When the injector fuel injection hole diameter hole does not change the number of hours, due to the resistance increase of sprayed oil injection angle increases, and each cam rotating angle of injection quantity decreases. At this point, due to the increasing pressures of high pressure tubing and are prone to repeated injection.
(3) high pressure oil pipe size
Long high pressure tubing, oil spraying large delay angle and Jet Yau continued basically unchanged. That is as high pressure tubing length increases, its actual fuel injection advance angle is smaller. If does not equal the length of each cylinder of high pressure tubing, you will make each cylinder injection vary, this is the effect of multi-cylinder diesel engine is not working even one reason. In order to make consistent cylinder injection, each cylinder of high pressure tubing length the same as much as possible.
Smaller tubing inner diameter, greater fuel flow resistance, oil spraying large delay angle.
(4) diesel engine load and speed
When the speed of diesel engine and fuel injection timing does not change, if the increased load, its fuel injection fuel injection end change starting point is essentially the same, and increased during the second half of the injection quantity.
When the load of diesel engine and fuel injection timing does not change when you change the speed, as the speed increases, the corresponding time shortening of each cam rotating angle, so fuel injection delays and injection angles are increasing, and each cam rotating angle of injection quantity reduction.
1, exception, Jet
(1) repeat injection (secondary injection)
When the end of the injection pump and oil, again after the injector needle valve seat was lifted by hydraulic spray phenomenon known as repeat injection, also known as secondary injection. This phenomenon in diesel engines under high speed loading condition most likely to occur. Disadvantages of repeated injection is on the one hand will make the injection angle larger, on the one hand because of late under low pressure fuel injection, resulting in deterioration of the reduced quality of atomization, combustion and smoke rise, parts overheating, such as bonded carbon in combustion chamber and exhaust black smoke, thereby reducing the reliability and economy of the diesel engine.
(2) intermittent injection
During the oil supply in fuel injection pump, injector needle valve intermittent opening and closing (frequent ups and downs), inadequate and insufficient lift, Jet, a phenomenon known as intermittent spraying. Its easy to occur under conditions of low speed.
(3) unstable Jet and alternate Jet
Unstable injection refers to the injection pump can continue working, but the oil circulating spray in spray changing circumstances. Their extreme lapse of time Jet, spray only twice in every oil fuel injector for fuel injection pump oil. This situation is occurring in diesel engines at low speed under low load conditions. When there were intervals when, a loop is not firing, so the gallop.
Second, diesel engine fuel injection pump and injectors
Requirements for fuel injection device
(1) fuel atomization
Good atomization of fuel, is the foundation of good combustion process, mainly by providing some fuel injection pressure of injection pump and injectors sprayed, and to guarantee. Higher fuel injection pressure, fog effects are better.
(2) to correct injection timing
To ensure the realization of good combustion process, to correct injection timing is also an important factor. For efficient combustion process, generally before the TDC will fuel injected into the cylinder. Fuel injected into the cylinders crank angle between the point and the ending point on, known as the "fuel injection advance angle", and pumps on the start point for oil and crank angle between the points. Known as the "fuel supply advance angle". Fuel injection device must to correct injection advance angle of fuel injected into the cylinder.
Fuel injection fuel supply advance angle of advance angle mainly by decision, and fuel supply advance angle is determined by the fuel injection pump cam to the installation location. Calibration conditions fuel supply advance angle of experimental determination by the factory. But Dang using of fuel quality change Shi, fuel of delay burning period occurs changes, above by requirements of for oil ahead of corner to again adjustment; also, more cylinder diesel engine due to spray pump and cam manufacturing Shang of difference and using in the of wear different, despite the spray pump cam of installed angle same, but the cylinder of actual for oil ahead of corner still has difference, so requirements the cylinder of spray oil timing can separate regulation. Adjust injection timing is mostly achieved through changing the installation position of cams on the camshaft.
(3) fuel delivery adjustments
Each cycle of the diesel engine in the amount of fuel injected into the cylinder size determines the power of diesel engine, in order to adapt to changes in engine load, fuel injection pumps should be able to adjust according to the load injection quantity, this kind of adjustment is known as "general tone". Multi-cylinder diesel engine, each cylinder injection quantity should be equal, or high load, some cylinders may overload due to fuel injection too much; and at low load, some less cylinder injection quantity might stop working. In theory, each cylinder fuel injection pump for oil should be the same, but due to differences in manufacturing and use of injection pump wear in different, and when installed improperly adjusted and other reasons, virtually impossible to uniform. Therefore, in addition to requests by the General call, also can be adjusted independently.
(4) other requirements
From the perspective of maintaining stable performance of diesel engines, ask the fuel injection device will succeed in making repeated injection, intermittent Jet injection, instability and isolation exceptions such as Jet spray.
From a trading perspective, requirements of fuel injection equipment reliable, convenient adjustment, can quickly stop oil.
Third, the diesel engine mixture formation and combustion
1, the main factors affecting fuel atomization
(1) fuel injection pressure
When the fuel injection pressure increases, improve atomization fineness and uniformity, fuel spray cone angle and range increased, improved quality of atomization.
(2) number of orifice hole
Nozzle total circulation area in the same case, the more many nozzle holes, its smaller diameter, atomization fineness and uniformity increase fuel spray cone angle increased, but declining range. Number and diameter of orifice hole is determined by the fuel spray and combustion chamber for the best match to.
(3) spray the hole diameter
When the orifice diameter increases, atomizing fineness and evenness are declining, but increases the range of fuel spray cone angle decreases. Instead, when the orifice diameter decreases, atomizing improve fineness and uniformity, reduce the range of fuel spray cone angle increases.
(4) fuel viscosity
When the oil viscosity increases, due to its poor mobility, divided more difficult, atomization from malnutrition.
(5) the Jet back pressure
When the Jet back pressure increases, the density of compressed air in the cylinder increases, when fuel injection was the resistance increases, improved quality of atomization, cone angle is larger, but shorten the range.
2, on the combustion process of diesel engine requirements
General requirements for diesel engine combustion process are: combustion totally smooth, speedy and timely, not gross, air a high utilization rate.
Four, diesel engine fault inspection
1, fuel pump main failure
Injection pump plunger sleeve are the main parts, valve and valve seat two precision coupling, so most of the major faults of injection pump occurs in two parts.
(1) the cavitation
In the fuel injection system, when a fuel pressure drops below or equal to the temperature of vaporization of fuel pressure, started the fuel gasification and bubble, followed by rupture of bubbles under positive pressure wave, and inspire very strong impact, effect on the metal surface. This repeated erosion, cavitation damage will cause a metal surface, making fuel injection system parts damaged. System locations most susceptible to cavitation in fuel injection pump valve and valve seat seal, pump body corresponding to the oil return holes, inner wall of high pressure oil pipe and injector needle valve seal.
Cavitation high pressure system can be resolved by selecting Uninstall volume of delivery valve, low-voltage system of cavitation, accessible through the increasing pressures of fuel oil or oil recovery setting in the system buffer solutions.
(2) excessive wear and tear, napping, piston and sleeve garter and bitten to death
Excessive wear of the piston and sleeve will degrade sealing, resulting in poor atomization of fuel injection pressure is reduced, non-uniform, the amount of each cylinder's injection and combustion issues of deterioration.
Piston clamping and bitten to death would cause the cylinder oil pump is not available for stopping work. Caused reason for clamping or bitten to death, mostly fuel cleaning bad quality, impurity particles in oil. In the particular case, or may be installed incorrectly or too small a gap, or excessive working temperatures, temperature changes caused by too fast.
(3) wear of valve and valve seat, valve stem stuck or killed
After the valve and valve seat wear, seal decline, caused decline in the residual pressure or high pressure pipeline injection quantity decrease, affecting the quality of atomization and combustion processes. Valve and valve seat wear caused by reasons, mainly oil impurities in fuel, acid corrosion, impact or valve distortion, and so on.
Stem clamping or bitten to death may be due to poor lubrication, unevenly, could also be valve rods and bushings resulting from deformation. Corresponding failures occurred because the valve does not properly. For example: stem valve open position stuck, then the return valve cannot be closed, making stops for fuel injection pump for oil.
2, checking and adjustment of fuel injection pump
Function of the injection pump is scheduled to fuel injector with a certain pressure, quantitative, so it should also be focused on sealing, check and adjust the timing and amount of oil for these three aspects.
(1) fuel pump seal check
Main check piston injection pump sealing sleeve parts, valve and inlet and outlet valves.
① comprehensive inspection
Fitted with pressure gauge at the exhaust tubing connector, shake the lever with your hand pump, when the oil reaches manual stop when under pressure
Pump oil, keep the piston position, watch the pressure gauge pressure. If the time specified in the instructions (usually a 30s) pressure remains unchanged, fuel injection pump sealing is considered good, otherwise, seal the bad.
When injection pump seals are found when bad, should be based on the construction of injection pump, outlet valve and inlet and back separately check valve and piston parts.
② outlet valve check
Outlet valve seal check procedures and comprehensive inspection of the same, but when under pressure in the hydraulic achieve statement,
Let the plunger naturally downward in order to specifically check out valve seal.
③ remove the outlet valve check
Valve is removed, check the comprehensive inspection procedure, mainly check the piston and intake, return valve seal
Sexual.
When totally worn out parts are found, should be renewed. Coupling grinding recovery.
(2) checking and adjustment of oil supply timing
Under optimal fuel supply advance angle of calibration experiment to determine and indicate the diesel engine by the factory manual, oil supply cam installed in order to ensure that most perspective prevails. However, when use of the fuel quality changes, fuel supply advance angle should be readjusted; in addition, each cylinder firing when not in uniform, to adjust the cylinder alone advance angle.
① oil supply timing of checks
Oil a, risking method
Bleed method in check when the injection timing should be removed on the injection pump high pressure oil pipe. Put on dedicated check oil
Tube. The throttle to the calibration oil supply position, several oil pump, tubing run after oil, will erase the flowlines surface. Then press the cars slowly turning, while complying with the outlet surface. When the liquid level began to rise this time scale the cylinder on the flywheel fuel supply advance angle.
This law only applies to small and medium diesel engines, larger piston diameter of diesel engine, fuel injection time shorter, due to this law room for larger errors, inappropriate use.
B, illumination method
Regulation of big oil return hole end type fuel injection pump, if the sleeve on the same high, oil return holes available illumination method for measuring time. Disassemble the pump body corresponding to the oil return holes on the screw slowly turning, with torch lighting from the oil hole. When the column just north of the Great Wall line oil hole covers back to see when the light, to stop turning, this time on the flywheel pointer indicates the scale of the oil pump and oil starting point, that is, fuel supply advance angle.
C, mark law
Some starting points for oil pump of diesel engine injection pump body equipped with fixed and sliding tag. When turning, from gap (Windows) see tags moment of coincidence, is the starting point of injection pump for oil.
② oil supply timing adjustment
Adjustment of oil supply timing achieved mainly through two channels: one way is to change the relative position of the cam and camshaft, changing the relationship between cam and crankshaft timing, so as to achieve change timing adjustment of oil supply; another way is to change the chute and plunger sleeve relative location oil return holes, change cam to work effectively to achieve oil supply timing adjustments. To change the relative positions of the chute and plunger sleeve, there are two ways to achieve: move the plunger up and down and up and down the sleeve. Adjustment of oil supply timing by rotating cams law

   （1）噴油規(guī)律

所謂噴油規(guī)律，是一個(gè)循環(huán)的噴油量在整個(gè)噴射延續(xù)時(shí)間內(nèi)的分配情況，即每度曲柄轉(zhuǎn)角噴出油量的分配曲線(xiàn)。

   （2）噴油延遲

噴油延遲主要是由于燃油的可壓縮性、高壓油管的彈性以及高壓油管中的波動(dòng)現(xiàn)象造成的。

4、影響噴油規(guī)律的因素

   （1）凸輪曲線(xiàn)和有效工作段

油泵凸輪型線(xiàn)決定了柱塞運(yùn)動(dòng)規(guī)律，而柱塞的迅速變化規(guī)律決定油泵的供油規(guī)律，從而影響噴油規(guī)律。在柱塞有效行程和供油始點(diǎn)相同的情況下，凸輪外形越陡，油壓上升越快，供油速度越大，噴油延遲角和噴油持續(xù)角就越小。

   （2）柱塞直徑和噴孔直徑

在不改變柱塞行程而增大柱塞直徑時(shí)，供油速度增大，噴油延遲角和持續(xù)角均減小，有利于燃燒在上止點(diǎn)附近結(jié)束，柴油機(jī)經(jīng)濟(jì)性變好。但初期的噴油速率提高，會(huì)使燃燒開(kāi)始時(shí)參加燃燒的油量增多，運(yùn)轉(zhuǎn)粗暴。

當(dāng)噴油器的孔數(shù)不變而噴油孔直徑變小時(shí)，由于噴油阻力的增加使噴油持續(xù)角增大，而每度凸輪轉(zhuǎn)角的噴油量減小。此時(shí)，由于高壓油管中的壓力增高，容易產(chǎn)生重復(fù)噴射。

   （3）高壓油管尺寸

高壓油管越長(zhǎng)，噴油延遲角越大而噴油持續(xù)角基本不變。也就是說(shuō)隨著高壓油管長(zhǎng)度的增加，其實(shí)際噴油提前角卻變小了。如果各缸高壓油管的長(zhǎng)度不相等，則將使各缸噴油規(guī)律有所差別，這也是影響多缸柴油機(jī)工作不均勻的原因之一。為了使各缸噴油規(guī)律一致，應(yīng)盡可能使各缸的高壓油管長(zhǎng)度相同。

油管內(nèi)徑越小，燃油流動(dòng)阻力越大，噴油延遲角越大。

   （4）柴油機(jī)負(fù)荷與轉(zhuǎn)速

當(dāng)柴油機(jī)轉(zhuǎn)速及噴油定時(shí)不變時(shí)，若增大負(fù)荷，其噴油始點(diǎn)基本不變而噴油終點(diǎn)改變，并且增加了后半期的噴油量。

當(dāng)柴油機(jī)負(fù)荷及噴油定時(shí)不變而改變轉(zhuǎn)速時(shí)，隨著轉(zhuǎn)速的增加，相應(yīng)每度凸輪轉(zhuǎn)角的時(shí)間縮短，故噴油延遲角和噴油持續(xù)角均增大，而每度凸輪轉(zhuǎn)角的噴油量減少。

1、  異常噴射

   （1）重復(fù)噴射（二次噴射）

當(dāng)噴油泵供油結(jié)束，噴油器針閥落座后有重新被油壓抬起的噴射現(xiàn)象稱(chēng)為重復(fù)噴射，又叫二次噴射。這種現(xiàn)象在柴油機(jī)高轉(zhuǎn)速大負(fù)荷的工況下最容易發(fā)生。重復(fù)噴射的缺點(diǎn)是一方面會(huì)使噴油持續(xù)角變大，另一方面由于后期在低壓下噴油、致使霧化質(zhì)量降低、燃燒惡化、排煙升高、機(jī)件過(guò)熱、燃燒室結(jié)碳、排氣冒黑煙等，從而降低了柴油機(jī)的可靠性和經(jīng)濟(jì)性。

   （2）斷續(xù)噴射

在噴油泵的一次供油期間，噴油器針閥斷續(xù)啟閉（頻繁地起落），而且起升不足、噴射不力，這種現(xiàn)象稱(chēng)為斷續(xù)噴射。其容易在低轉(zhuǎn)速的工況下發(fā)生。

   （3）不穩(wěn)定噴射和隔次噴射

不穩(wěn)定噴射是指噴油泵雖能持續(xù)工作，但各循環(huán)噴油量在噴射時(shí)不斷變動(dòng)的情況。其極端的情況時(shí)隔次噴射，即噴油泵每供油兩次噴油器才噴一次油。這種情況也是在柴油機(jī)低速低負(fù)荷的工況下發(fā)生的。當(dāng)發(fā)生隔次噴射時(shí)，一個(gè)循環(huán)不發(fā)火，故運(yùn)轉(zhuǎn)不穩(wěn)定。

二、柴油發(fā)動(dòng)機(jī)噴油泵及噴油器

對(duì)噴油設(shè)備的要求

   （1）燃油的霧化

燃油的良好霧化，是實(shí)現(xiàn)良好燃燒過(guò)程的基礎(chǔ)，主要靠噴油泵提供的一定噴油壓力和噴油器噴和來(lái)保證。噴油壓力越高，霧化效果越好。

   （2）正確地噴油定時(shí)

要保證實(shí)現(xiàn)良好的燃燒過(guò)程，正確地噴油定時(shí)也是一個(gè)重要的因素。為實(shí)現(xiàn)高效的燃燒過(guò)程，一般均在上止點(diǎn)前就將燃油噴入氣缸。燃油噴入氣缸點(diǎn)與上止點(diǎn)之間的曲柄轉(zhuǎn)角，稱(chēng)為“噴油提前角”，而油泵開(kāi)始供油點(diǎn)與上止點(diǎn)之間的曲柄轉(zhuǎn)角。稱(chēng)為“供油提前角”。噴油設(shè)備必須以正確的噴油提前角將燃油噴入氣缸。

噴油提前角主要由供油提前角決定，而供油提前角則由噴油泵凸輪的安裝位置來(lái)決定。在標(biāo)定工況下的供油提前角由工廠試驗(yàn)確定。但是當(dāng)使用的燃油品質(zhì)變更時(shí)，燃油的滯燃期發(fā)生變化，上述所要求的供油提前角要重新調(diào)整；另外，多缸柴油機(jī)由于噴油泵和凸輪制造上的差別和使用中的磨損不同，盡管各噴油泵凸輪的安裝角度相同，但各缸的實(shí)際供油提前角仍有差別，故要求各缸的噴油定時(shí)能單獨(dú)調(diào)節(jié)。調(diào)節(jié)噴油定時(shí)大多是通過(guò)改變凸輪在凸輪軸上的安裝位置來(lái)實(shí)現(xiàn)的。

   （3）供油量的調(diào)節(jié)

在柴油機(jī)每循環(huán)中噴入汽缸的燃油量決定著柴油機(jī)的功率大小，為適應(yīng)柴油機(jī)負(fù)荷的變化，噴油泵應(yīng)能根據(jù)負(fù)荷來(lái)調(diào)節(jié)噴油量，此種調(diào)節(jié)稱(chēng)為“總調(diào)”。在多缸柴油機(jī)中，各缸噴油量應(yīng)該均等，否則在高負(fù)荷時(shí)，某些氣缸可能因噴油量過(guò)多而超負(fù)荷；而在低負(fù)荷時(shí)，某些氣缸可能因噴油量少而停止工作。理論上，各缸噴油泵的供油量應(yīng)該是一樣的，但由于噴油泵制造上的差別和使用中磨損的不同，以及安裝時(shí)調(diào)節(jié)不當(dāng)?shù)仍?，?shí)際上不可能均勻。因此，除了要求由總調(diào)外，還應(yīng)可以進(jìn)行單獨(dú)調(diào)節(jié)。

   （4）其它要求

從保持柴油機(jī)性能穩(wěn)定的角度出發(fā)，要求噴油設(shè)備能根絕重復(fù)噴射、斷續(xù)噴射、不穩(wěn)定噴射和隔次噴射等異常噴射現(xiàn)象。

從營(yíng)運(yùn)角度出發(fā)，要求噴油設(shè)備工作可靠、調(diào)節(jié)方便、能迅速停油。

三、柴油發(fā)動(dòng)機(jī)混合氣的形成和燃燒

1、影響燃油的霧化的主要因素

   （1）噴油壓力

當(dāng)噴油壓力增大時(shí)，霧化細(xì)度及均勻度提高，油束錐角和射程增大，霧化質(zhì)量提高。

   （2）噴孔孔數(shù)

在噴油嘴總流通面積不變的情況下，噴孔孔數(shù)越多，其直徑越小，霧化細(xì)度和均勻性提高，油束錐角增大，但射程下降。故噴孔孔數(shù)和直徑是是由油束與燃燒室獲得最佳匹配來(lái)決定的。

   （3）噴孔直徑

當(dāng)噴孔直徑增大時(shí)，霧化細(xì)度和均勻度均下降，但油束射程增大而錐角減小。相反，當(dāng)噴孔直徑減小時(shí)，霧化細(xì)度及均勻度提高，油束錐角增大而射程減小。

   （4）燃油粘度

當(dāng)燃油粘度增加時(shí)，由于其流動(dòng)性差，分裂較困難，故霧化不良。

   （5）噴射背壓

當(dāng)噴射背壓增加時(shí)，即缸內(nèi)壓縮空氣的密度增加，燃油噴射時(shí)受到的阻力增加，因此霧化質(zhì)量提高，錐角變大，但射程縮短。

2、柴油機(jī)對(duì)燃燒過(guò)程的要求

對(duì)柴油機(jī)燃燒過(guò)程的總要求是：燃燒完全、迅速及時(shí)、工作平穩(wěn)不粗暴、空氣利用率高。

四、柴油發(fā)動(dòng)機(jī)故障檢驗(yàn)

1、噴油泵的主要故障

噴油泵的主要零件是柱塞套筒、閥及閥座兩對(duì)精密偶件，因此噴油泵的主要故障大多發(fā)生在這兩對(duì)零件上。

   （1）穴蝕

在燃油噴射系統(tǒng)中，當(dāng)某處的燃油壓力下降到低于或等于該溫度下的燃油汽化壓力時(shí)，該處燃油就開(kāi)始?xì)饣a(chǎn)生氣泡，隨后氣泡在正壓力波的作用下破裂，并激發(fā)出很強(qiáng)的沖擊力，作用在金屬壁面上。這樣反復(fù)地侵蝕，就會(huì)引起金屬表面穴蝕破壞，使噴油系統(tǒng)零件損壞。系統(tǒng)中最易發(fā)生穴蝕的地點(diǎn)有噴油泵閥與閥座的密封處、與回油孔相對(duì)應(yīng)的泵體、高壓油管內(nèi)壁及噴油器針閥密封處。

高壓系統(tǒng)中的穴蝕可通過(guò)選擇出油閥的卸載容積來(lái)解決，低壓系統(tǒng)中的穴蝕，可通過(guò)提高進(jìn)油腔的燃油壓力或在回油系統(tǒng)中設(shè)置緩沖器的方法來(lái)解決。

   （2）柱塞和套筒過(guò)度磨損、拉毛、卡緊和咬死

柱塞和套筒的過(guò)度磨損會(huì)使密封性下降，造成噴油壓力降低、霧化不良、各缸噴油量不均勻和燃燒惡化等問(wèn)題。

柱塞卡緊和咬死會(huì)引起油泵不能供油而使氣缸停止工作。造成卡緊或咬死的原因，大多是燃油凈化質(zhì)量不良，油中應(yīng)有雜質(zhì)顆粒。在個(gè)別情況下，也可能是安裝不正確或間隙過(guò)小，或工作溫度過(guò)高，溫度變化過(guò)快所致。

   （3）閥和閥座磨損、閥桿卡死或咬死

閥和閥座磨損后，密封性下降，使高壓油管中的剩余壓力下降或造成噴油量減小，影響霧化質(zhì)量及燃燒過(guò)程。造成閥和閥座磨損的原因，主要是油中有雜質(zhì)、燃油的酸性腐蝕、撞擊或閥面扭曲變形等。

閥桿卡緊或咬死的原因可能是潤(rùn)滑不良、受熱不均，也可能是閥桿及導(dǎo)套變形而引起。這時(shí)將會(huì)因閥不能正確動(dòng)作而發(fā)生相應(yīng)的故障。例如：閥桿在閥開(kāi)啟位置卡死，則回油閥不能關(guān)閉，使噴油泵停止供油。

2、噴油泵的檢查與調(diào)整

噴油泵的功能是定時(shí)、定量地向噴油器提供一定壓力的燃油，所以對(duì)它的檢查和調(diào)整也應(yīng)著重在密封性、定時(shí)及供油量這三個(gè)方面。

   （1）噴油泵密封性檢查

噴油泵密封性主要檢查柱塞套筒偶件、出油閥偶件及進(jìn)、出油閥。

①     綜合檢查

在排油管接頭處裝上壓力表，用手搖動(dòng)杠桿油泵，當(dāng)油壓達(dá)到說(shuō)明書(shū)規(guī)定的壓力時(shí)停

止泵油，保持柱塞位置，觀看壓力表的壓力。如果在說(shuō)明書(shū)規(guī)定的時(shí)間（一般為30s）內(nèi)壓力保持不變，則認(rèn)為噴油泵密封良好，否則密封不良。

當(dāng)發(fā)現(xiàn)噴油泵密封不良時(shí)，應(yīng)根據(jù)噴油泵的構(gòu)造，分別對(duì)出油閥和進(jìn)、回油閥以及柱塞偶件進(jìn)行檢查。

②     出油閥檢查

出油閥的密封性檢查的步驟與綜合檢查相同，只是在油壓達(dá)到說(shuō)明書(shū)規(guī)定的壓力時(shí)，

讓柱塞自然下行，以便專(zhuān)門(mén)檢查出油閥的密封性。

③     取出出油閥檢查

取出出油閥后，按綜合檢查的步驟進(jìn)行檢查，主要檢查柱塞偶件及進(jìn)、回油閥的密封

性。

    當(dāng)發(fā)現(xiàn)磨損過(guò)度的零件時(shí)，應(yīng)予換新。偶件應(yīng)研磨恢復(fù)。

   （2）供油定時(shí)的檢查與調(diào)整

標(biāo)定工況下的最佳供油提前角由工廠試驗(yàn)確定并注明在柴油機(jī)的說(shuō)明書(shū)上，供油凸輪的安裝以保證這個(gè)最擠角度為準(zhǔn)。但是，當(dāng)使用的燃油品質(zhì)變更時(shí)，供油提前角應(yīng)重新調(diào)節(jié)；另外，各缸發(fā)火不均勻時(shí)，要單獨(dú)調(diào)整各缸提前角。

①     供油定時(shí)的檢查

A、冒油法

在采用冒油法檢查噴油定時(shí)的時(shí)候，應(yīng)拆去噴油泵上的高壓油管。換上專(zhuān)用的檢查油

管。將油門(mén)置于標(biāo)定供油位置，先使油泵供幾次油，待油管冒油后，將出油管液面抹平。然后按正車(chē)方向慢慢盤(pán)車(chē)，同時(shí)注意出油口液面。當(dāng)液面開(kāi)始上升這一時(shí)刻飛輪上的刻度即為該缸的供油提前角。

此法只適用于中小型柴油機(jī)，對(duì)于柱塞直徑較大、噴油時(shí)間較短的柴油機(jī)，由于此法容易出現(xiàn)較大的誤差而不宜采用。

B、照光法

對(duì)大型回油孔終點(diǎn)調(diào)節(jié)式噴油泵，若套筒上有同樣高的進(jìn)、回油孔，可用照光法測(cè)量定時(shí)。拆下泵體上與進(jìn)回油孔相對(duì)應(yīng)的螺釘，緩緩盤(pán)車(chē)，從油孔處用手電筒照明。當(dāng)柱塞上行剛好將回油孔遮住而看不到光線(xiàn)時(shí)，馬上停止盤(pán)車(chē)，此時(shí)飛輪上指針?biāo)甘镜目潭燃礊樵撚捅玫墓┯褪键c(diǎn)，亦即供油提前角。

C、標(biāo)記法

有些柴油機(jī)噴油泵的供油始點(diǎn)在泵體上裝有固定和滑動(dòng)標(biāo)記。盤(pán)車(chē)時(shí)，當(dāng)從缺口（窗口）處看標(biāo)記重合的瞬間，即為噴油泵的供油始點(diǎn)。

② 供油定時(shí)的調(diào)節(jié)

供油定時(shí)的調(diào)節(jié)主要通過(guò)兩條途徑來(lái)實(shí)現(xiàn)：一條途徑是改變凸輪與凸輪軸的相對(duì)位置，改變凸輪與曲軸的定時(shí)關(guān)系，從而達(dá)到改變定時(shí)供油的調(diào)節(jié)；另一條途徑是改變柱塞斜槽與套筒回油孔的相對(duì)位置，改變凸輪的有效工作段來(lái)實(shí)現(xiàn)供油定時(shí)調(diào)整。而要改變柱塞斜槽與套筒的相對(duì)位置，又有兩種方法可以達(dá)到：上下移動(dòng)柱塞和上下移動(dòng)套筒。故供油定時(shí)的調(diào)節(jié)有轉(zhuǎn)動(dòng)凸輪法、升降柱塞法及升降套筒法等三種。

A、轉(zhuǎn)動(dòng)凸輪法

凸輪軸是由曲軸帶動(dòng)的，兩者之間存在著一定的定時(shí)關(guān)系，當(dāng)凸輪與凸輪軸固定時(shí)，凸輪與曲軸之間亦有定時(shí)關(guān)系。而當(dāng)改變凸輪與凸輪軸的相對(duì)位置時(shí)，凸輪與曲軸的定時(shí)關(guān)系也就改變了。轉(zhuǎn)動(dòng)凸輪法就是以此為基礎(chǔ)進(jìn)行供油定時(shí)調(diào)整的。

大中型柴油機(jī)中凸輪在凸輪軸上的固定方法，一般采用錐面齒定位、鎖緊螺母壓緊的方法實(shí)現(xiàn)。當(dāng)調(diào)整凸輪與凸輪軸相對(duì)位置時(shí)，只要松開(kāi)鎖緊螺母，按需要轉(zhuǎn)動(dòng)凸輪后再上緊鎖緊螺母即可。順著凸輪軸旋轉(zhuǎn)方向轉(zhuǎn)動(dòng)凸輪，則供油提前角增大，反之則減小。

B、升降柱塞法

升降柱塞法多用于中小型柴油機(jī)回油孔調(diào)節(jié)式噴油泵。升降柱塞，使得柱塞斜槽封閉回油孔的時(shí)刻發(fā)生變化，從而實(shí)現(xiàn)噴油定時(shí)的調(diào)整。

C、升降套筒法

升降套筒法與升降柱塞法類(lèi)似，可用于回油孔調(diào)節(jié)式噴油泵。

3、噴油器的主要故障

   （1）針閥偶件的磨損、漏油和卡緊

   （2）噴孔磨損、結(jié)碳、阻塞和裂紋