Many researchers believe that because hydrogen fuel is prone to spontaneous combustion, the engine does not need to use the pre combustion chamber spark plug when burning hydrogen fuel, because this component will reduce the safety of hydrogen fuel combustion. However, the actual situation is just the opposite. In order to achieve the goal of zero emission, the hydrogen mixture is relatively thin and the mixture λ> 2.5。 Under this condition, the spontaneous combustion of hydrogen fuel will be significantly reduced, so its combustion speed will be reduced accordingly.

研究人員通過(guò)采用經(jīng)優(yōu)化設(shè)計(jì)的預(yù)燃室火花塞，改善了該類(lèi)稀薄混合氣的燃燒速度。與此相反，存在缺陷的預(yù)燃室火花塞在燃用氫燃料時(shí)會(huì)導(dǎo)致一系列技術(shù)弊端，從而降低了預(yù)燃室火花塞用于氫發(fā)動(dòng)機(jī)的適用性。

The researchers improved the combustion speed of this kind of lean mixture by using the optimized pre combustion chamber spark plug. On the contrary, the defective precombustion chamber spark plug will lead to a series of technical disadvantages when burning hydrogen fuel, which reduces the applicability of precombustion chamber spark plug for hydrogen engine.

對(duì)應(yīng)用預(yù)燃室火花塞的挑戰(zhàn)在于所開(kāi)發(fā)的預(yù)燃室火花塞必須能有效平衡發(fā)動(dòng)機(jī)在燃用天然氣和氫燃料時(shí)的所有目標(biāo)沖突。設(shè)計(jì)這種火花塞的核心技術(shù)是預(yù)燃室的主動(dòng)掃氣過(guò)程。研究人員借助于1個(gè)可側(cè)面貫穿預(yù)燃室的較長(zhǎng)直孔，即可將新鮮混合氣導(dǎo)入至電極間隙附近，在形成火焰束之前就使其在預(yù)燃室中進(jìn)行充分燃燒。

The challenge for the application of precombustion chamber spark plugs is that the developed precombustion chamber spark plugs must be able to effectively balance all target conflicts when the engine burns natural gas and hydrogen fuel. The core technology of designing this spark plug is the active scavenging process of the precombustion chamber. With the help of a long straight hole that can pass through the precombustion chamber on the side, the researchers can introduce the fresh mixture near the electrode gap and fully burn it in the precombustion chamber before forming the flame beam.

同時(shí)，研究人員采用了CFD模擬軟件來(lái)優(yōu)化預(yù)燃室參數(shù)(預(yù)燃室?guī)缀螌W(xué)、容積、噴孔方向和其他參數(shù))，以達(dá)到所期望的λ數(shù)值和流動(dòng)速度。特別是使預(yù)燃室內(nèi)的混合氣濃度比主燃燒室內(nèi)更稀，以便減小氫燃料自燃的傾向。缸內(nèi)混合氣必須有著較高的流動(dòng)速度，以便使可燃混合氣在燃燒時(shí)具有足夠的冷卻效果，同時(shí)防止天然氣在250 mg/Nm3的濃度運(yùn)行時(shí)導(dǎo)致的火焰熄滅。佳的預(yù)燃室設(shè)計(jì)可通過(guò)預(yù)燃室內(nèi)的完全燃燒而產(chǎn)生強(qiáng)烈的火焰束，從而確保主燃燒室內(nèi)的火焰?zhèn)鞑ミ^(guò)程更為迅速和均勻。

At the same time, the researchers used CFD simulation software to optimize the precombustion chamber parameters (precombustion chamber geometry, volume, orifice direction and other parameters) to achieve the desired results λ Numerical and flow velocity. In particular, the mixture concentration in the precombustion chamber is thinner than that in the main combustion chamber, so as to reduce the tendency of spontaneous combustion of hydrogen fuel. The mixture in the cylinder must have a high flow speed, so that the combustible mixture can have sufficient cooling effect during combustion, and prevent the flame extinction caused by the operation of natural gas at the concentration of 250 mg / Nm3. The good precombustion chamber design can produce a strong flame beam through the complete combustion in the precombustion chamber, so as to ensure that the flame propagation process in the main combustion chamber is more rapid and uniform.

由于發(fā)動(dòng)機(jī)配備了氣缸壓力測(cè)量裝置，因此研究人員更易于識(shí)別缸內(nèi)的燃燒狀況。圖6示出了所有6個(gè)氣缸使用標(biāo)準(zhǔn)火花塞和Prometheus預(yù)燃室火花塞時(shí)的燃燒壓力數(shù)據(jù)。正如預(yù)計(jì)，后者的燃燒壓力波動(dòng)有所降低。據(jù)此就能證實(shí)發(fā)動(dòng)機(jī)在燃用氫燃料時(shí)仍具有較高的工作能力。

Because the engine is equipped with a cylinder pressure measuring device, it is easier for researchers to identify the combustion conditions in the cylinder. Figure 6 shows the combustion pressure data for all six cylinders using standard spark plugs and Prometheus precombustion chamber spark plugs. As expected, the combustion pressure fluctuation of the latter is reduced. Therefore, it can be confirmed that the engine still has high working capacity when burning hydrogen fuel.

研究人員已通過(guò)天然氣進(jìn)行過(guò)相似的試驗(yàn)過(guò)程，并與原始設(shè)備制造商(OEM)生產(chǎn)的預(yù)燃室火花塞進(jìn)行了比較。在采用了Prometheus預(yù)燃室火花塞后，缸內(nèi)展現(xiàn)出較為穩(wěn)定和迅速的燃燒過(guò)程，特別是在排放量為500 mg/Nm3的情況下運(yùn)行時(shí)，整機(jī)效率提高了0.3%。

Researchers have conducted a similar test process with natural gas and compared it with the pre combustion chamber spark plugs produced by the original equipment manufacturer (OEM). After using Prometheus precombustion chamber spark plug, the cylinder shows a relatively stable and rapid combustion process, especially when the emission is 500 mg / Nm3, the overall efficiency is increased by 0.3%.

在排放量為250 mg/Nm3的情況下運(yùn)行時(shí)，整機(jī)效率提高了0.4%，而且在排放量為200 mg/Nm3的情況下運(yùn)行時(shí)，離爆燃極限的裕量進(jìn)一步增大，使用天然氣運(yùn)行時(shí)的稀薄極限與此相似。研究人員在證實(shí)了Prometheus預(yù)燃室火花塞具有預(yù)期的工作能力之后，后續(xù)仍需要對(duì)其進(jìn)行耐久性試驗(yàn)。

When the emission is 250 mg / Nm3, the efficiency of the whole machine is improved by 0.4%, and when the emission is 200 mg / Nm3, the margin from the deflagration limit is further increased. The rarefaction limit when using natural gas is similar. After the researchers confirmed that the Prometheus precombustion chamber spark plug has the expected working capacity, the durability test still needs to be carried out later.