Viewing 1 to 11 of 11
Journal Article
Akira Iijima, Takuya Izako, Takahiro Ishikawa, Takahiro Yamashita, Shuhei Takahata, Hiroki Kudo, Kento Shimizu, Mitsuaki Tanabe, Hideo Shoji
Engine knock is the one of the main issues to be addressed in developing high-efficiency spark-ignition (SI) engines. In order to improve the thermal efficiency of SI engines, it is necessary to develop effective means of suppressing knock. For that purpose, it is necessary to clarify the mechanism generating pressure waves in the end-gas region. This study examined the mechanism producing pressure waves in the end-gas autoignition process during SI engine knock by using an optically accessible engine. Occurrence of local autoignition and its development process to the generation of pressures waves were analyzed under several levels of knock intensity. The results made the following points clear. It was observed that end-gas autoignition seemingly progressed in a manner resembling propagation due to the temperature distribution that naturally formed in the combustion chamber. Stronger knock tended to occur as the apparent propagation speed of autoignition increased.
Technical Paper
Hyota Hoshino, Tatsuya Sato, Shuntaro Takano, Yuya Motoki, Hiroto Tanaka, Yuya Higuchi, Akira Iijima, Tomohiko Asai, Mitsuaki Tanabe, Yoshito Ashizawa, Junichi Sekiguchi, Hideo Shoji
This study focused on a non-equilibrium plasma discharge as a means of assisting HCCI combustion.Experiments were conducted with a four-stroke single-cylinder engine fitted with a spark electrode in the top of the combustion chamber for continuously generating non-equilibrium plasma from the intake stroke to the exhaust stroke. The results showed that applying non-equilibrium plasma to the HCCI test engine advanced the main combustion period that otherwise tended to be delayed as the engine speed was increased. In addition, it was found that the combined use of exhaust gas recirculation and non-equilibrium plasma prevented a transition to partial combustion while suppressing cylinder pressure oscillations at high loads.
Technical Paper
Yuki Yoshida, Kotaro Takeda, Zhimin Lin, Masanori Yamada, Akira Iijima, Mitsuaki Tanabe, Hideo Shoji
Abstract Improving the thermal efficiency of internal combustion engines requires operation under a lean combustion regime and a higher compression ratio, which means that the causes of autoignition and pressure oscillations in this operating region must be made clear. However, there is limited knowledge of autoignition behavior under lean combustion conditions. Therefore, in this study, experiments were conducted in which the ignition timing and intake air temperature (scavenging temperature) of a 2-stroke optically accessible test engine were varied to induce autoignition under a variety of conditions. The test fuel used was a primary reference fuel with an octane rating of 90. The results revealed that advancing the ignition timing under lean combustion conditions also advanced the autoignition timing, though strong pressure oscillations on the other hand tended not to occur.
Technical Paper
Masanori Yamada, Junki Sahara, Takashi Shimada, Yuki Yoshida, Chibin Rin, Akira Iijima, Tomohiko Asai, Mitsuaki Tanabe, Hideo Shoji
It is difficult to control the ignition timing of Homogeneous Charge Compression Ignition (HCCI) engines because they lack a physical means of igniting the mixture. Another issue of HCCI engines is their narrow operating range owing to the occurrence of misfiring at low loads and abnormal combustion at high loads. As a possible solution to these issues, this study focused on the generation of a streamer discharge using nonequilibrium plasma as a means of assisting HCCI combustion. A two-stroke engine that allowed visualization of the entire bore area was used in this study. A primary reference fuel blend (50 RON) was used as the test fuel. The streamer discharge was continuously generated in the end-gas region during a 360 deg. interval from the scavenging stroke to the exhaust stroke using a spark plug from which the ground electrode had been removed. Experiments were conducted in which the applied voltage of the streamer discharge was varied to investigate its effect on combustion.
Technical Paper
Naoya Watanabe, Takashi Kohata, Aiko Nakagawa, Mitsuaki Tanabe
The influence of the eddy scale of initial turbulence in RCM on the pressure rise rate after spontaneous ignition of end gas was investigated. The combustion time of the end gas after spontaneous ignition was observed by using high-speed direct photography. As a result, the large scale eddy reduced the pressure rise rate after spontaneous ignition. The temperature inhomogeneity of end gas was higher with the large scale eddy. The combustion time of end gas after spontaneous ignition was prolonged by variation in local ignition delay due to inhomogeneity. The large scale eddy may prevented the knocking occurrence.
Technical Paper
Naoya Ito, Akira Iijima, Akira Terashima, Junki Sahara, Takashi Shimada, Masanori Yamada, Tomohiko Asai, Mitsuaki Tanabe, Koji Yoshida, Hideo Shoji
Abstract This study investigated the effect of streamer discharge on autoignition and combustion in a Homogeneous Charge Compression Ignition (HCCI) engine. A continuous streamer discharge was generated in the center of the combustion chamber of a 2-stroke optically accessible engine that allowed visualization of the entire bore area. The experimental results showed that the flame was initiated and grew from the vicinity of the electrode under the application of a streamer discharge. Subsequently, rapid autoignition (HCCI combustion) occurred in the unburned mixture in the end zone, thus indicating that HCCI combustion was accomplished assisted by the streamer discharge. In other word, ignition timing of HCCI combustion was advanced after the streamer discharging process, and the initiation behavior of the combustion flame was made clear under that condition.
Journal Article
Akira Iijima, Mitsuaki Tanabe, Koji Yoshida, Hideo Shoji, Naoya Itoh, Akira Terashima, Tomoya Tojo
Combustion experiments were conducted with an optically accessible engine that allowed the entire bore area to be visualized for the purpose of making clear the characteristics that induce extremely rapid HCCI combustion and knocking accompanied by cylinder pressure oscillations. The HCCI combustion regime was investigated in detail by high-speed in-cylinder visualization of autoignition and combustion and emission spectroscopic measurements. The results revealed that increasing the equivalence ratio and advancing the ignition timing caused the maximum pressure rise rate and knocking intensity to increase. In moderate HCCI combustion, the autoignited flame was initially dispersed temporally and spatially in the cylinder and then gradually spread throughout the entire cylinder.
Technical Paper
Tomohiro Hasegawa, Masamitsu Kinoshita, Toru Arima, Kou Sato, Mitsuaki Tanabe
Homogeneous Charge Compression Ignition combustion in homogenized temperature fields was investigated experimentally using a super rapid compression machine. Temperature fields before a blue flame occurs are thought to control the burning process. The time of blue flame occurrence, burn rate and ignition delay time were measured. Temperature homogeneity before a blue flame occurred was controlled by two means. One was by the piston shape which controlled the roll-up vortex and the other was by the heat release of low temperature reactions that has a homogenizing effect. It was found that homogenized temperature fields contribute to the occurrence of a homogeneous blue flame while inhomogeneous fields produce an uneven occurrence.
Technical Paper
Masato Katsumata, Koji Morikawa, Mitsuaki Tanabe
Behaviors of shock waves in knocking phenomena were observed in detail and influences of low temperature reaction on the flame and spontaneous ignition of end gas were investigated through experiments using high-speed direct and schlieren photography. As a result, it was found that light emission of shock waves, that is an indicator of pressure, rose when the shock waves collided with the cylinder wall and that pressure waves arose by low temperature reaction before knocking occurrence. Flame oscillation was caused by pressure waves. It is presumed that pressure waves influence spontaneous ignition.
Technical Paper
Yusuke Watanabe, Koji Morikawa, Takuo Kuwahara, Mitsuaki Tanabe
We had improved RCM and developed a Super Rapid Compression Machine (SRCM) that realizes an extremely rapid compression compared with the conventional RCM. In this study, the performance of the developed SRCM was evaluated. The SRCM was used to investigate on the effects of equivalence ratio on HCCI of n-heptane and iso-octane fuel/air mixture. Experimental results for ignition delay time, τ, and combustion time, t, were obtained from the cylinder pressure histories. The HCCI at high engine speeds was clarified by Optical observation using a high speed camera. As a result, the ignition delay time and combustion time are found to saturate above equivalence ratio of 0.6 at constant compression ratio. In the HCCI combustion in high compression ratio case, shock wave occurs from the core region of the roll-up vortex cause by piston motion. The HCCI combustion has many peaks over a wide range of frequency.
Technical Paper
Koji Murakami, Mitsuaki Tanabe, Kiyoshi Aoki
We examined if air fuel ratio could be estimated by engine sound for a two-stroke glow engine. A time resolved FFT (Fast Fourier Transform) was adopted to analyze the engine sound. As a result, strong acoustic radiation were shown twice at TDC and BDC in the frequency range below 2.5 kHz in each cycle. For the case of high air fuel ratio, a peak of sound pressure in the range of 2.5 to 5 kHz exists in between TDC and BDC. This sound is supposed to be a noise due to anomalous combustion. Since the noise appears just after the combustion noise, the anomalous combustion noise is supposed to be a knocking noise. When the periodic noise in the range up to 2.5 kHz appears weakly twice in one cycle, the air fuel ratio is approaching low limit for a stable run of the engine at 12000 rpm. When the periodic noise in the range of 2.5 to 5 kHz appears once in one cycle between the periodic noise in the range up to 2.5 kHz, the air fuel ratio is approaching high limit.
Viewing 1 to 11 of 11