Tianjin team proposes reactivity controlled turbulent jet ignition to extend EGR tolerance and improve performance; ammonia potential
Researchers at Tianjin University have proposed a reactivity controlled turbulent jet ignition (RCTJI) based on a newly air-assisted pre-chamber turbulent jet ignition with a scavenging function to improve the reactivity in the pre-chamber.
In an open-access paper in the journal Fuel, they report that RCTJI with scavenged TJI can effectively extend EGR tolerance and improve spark ignition engine performance. They note that the concept of RCTJI can be further used in an ammonia-fueled engine to solve the issues of difficult ignition and slow flame propagation.
Air-assisted pre-chamber configuration. Zhou et al.
In the terms of RCTJI concept, hydrogen as a high reactivity fuel replaced of low reactivity fuel also can be injected in pre-chamber to control the reactivity.
Improving the thermal efficiency of internal combustion engines and reducing the carbon dioxide (CO2) emissions have become the subject of research in the face of increasingly stringent emissions and fuel consumption regulations, drawing increasing attention due to the ability of lean and dilute combustion to reduce fuel consumption and emissions. As an effective technique, the exhaust gas recirculation (EGR) method has been extensively studied and widely used in the field of internal combustion engines to lower the propensity of knock and NOx emission.
EGR is also can be considered as lean combustion with main CO2 dilution compared to the excess air dilution. EGR dilution can make the use of a three-way catalytic converter (TWC) possible. However, EGR can reduce the combustion temperature and flame propagation velocity, which deteriorates combustion stability and engine power. In the light of this issue, turbulent jet ignition is introduced to ensure reliable ignition and a high burning rate in spark-ignition engines by using a pre-chamber, which is receiving increasing attention in its application in SI engines.
… the objective of this work is to conduct experimental studies of the gasoline engine with EGR dilution combustion based on reactivity controlled turbulent jet ignition (RCTJI). As our knowledge, this study demonstrates the following new contributions: (1) the reactivity controlled turbulent jet ignition (RCTJI) is proposed based on a newly designed air-assisted pre-chamber configuration with a scavenging function (scavenged TJI) for the first time, to the best of the author’s knowledge. (2) The EGR tolerance is tested based on the RCTJI mode. (3) The different ignition modes involving spark ignition (SI), passive TJI, active TJI, and scavenged TJI are compared in terms of the combustion phases, fuel consumption, and pressure oscillation at different EGRs to reveal the in-depth mechanism. The present work will provide a very effective method to control the TJI intensity of pre-chamber.—Zhou et al.
The researchers used a four-stroke 0.5L single-cylinder engine, an electric dynamometer, a self-designed jet ignition system, and a dual direct injection fuel supply system for the main combustion chamber and pre-chamber, and a pressure test system. The experiment was carried out at the engine speed of 1500 rpm with a compression ratio of 11. The engine was naturally aspirated with an intake pressure of 1 bar and an intake temperature of 300 K. Zhou et al.
The results showed that three TJI modes can obviously shorten the combustion duration due to the fast jet flame.
Compared to the SI mode, the spark timing of TJI is not sensitive to the change in EGR rate. In particular, scavenged TJI could effectively promote the chemical reactivity in the pre-chamber, and subsequently improves the intensity of the turbulent jet flame and shortens the ignition delay and combustion duration. As a result, using scavenged TJI can effectively reduce cycle variation and achieve the lowest indicated specific fuel consumption (ISFC) at high EGR rates.
The main findings of the study were:
In general, the in-cylinder pressure rises rapidly shortly after ignition for the TJI due to the multi-point ignition and high-speed turbulent combustion in the main combustion chamber caused by the turbulent jet flame in the pre-chamber, compared to SI mode. The ignition delay and the combustion duration increase with the increase of the EGR rate in the four ignition modes. The TJI can effectively shorten the ignition delay and the combustion duration. Furthermore, it also can be seen that the increase of the EGR rate has a great influence on the spark timing of SI, while the spark timing of TJI is not sensitive to the evolution of EGR rate due to the shorter ignition delay time, which is also beneficial to the combustion stability.
For scavenged TJI, at high EGR rates, this mode can effectively reduce the exhaust gas rate, which improves ignition stability in the pre-chamber. It will also form a strong hot jet through the pre-chamber, which promotes combustion efficiency. Therefore, the scavenged TJI can achieve the lowest ISFC. The ISFC (235.7 g/kWh) of the scavenged TJI is reduced by 5.1%, 2.1%, and 0.7% compared to the SI, the active TJI, and the passive TJI, respectively. The heat loss of the pre-chamber also contributes to the high ISFC at the EGR of 0%.
The TJI combustion performs low cycle-to-cycle variation. The TJI mode also lowers the stochastic nature of the knock cycle compared to the SI mode. The combustion stability in the main combustion chamber can be improved and the COV can be significantly reduced by using the scavenged TJI, which effectively extends the EGR tolerance. The COVs at the EGR rates of 25.2% and 30.7% are 1.6% and 4.6%, respectively.
Lei Zhou, Yixiong Ding, A. Qian Li, Yuntong Song, Zongkuan Liu, Haiqiao Wei (2022) “Experimental study of gasoline engine with EGR dilution based on reactivity controlled turbulent jet ignition (RCTJI),” Fuel, Volume 331, Part 1, doi: 10.1016/j.fuel.2022.125744