Study on Improvement of Mixture Formation in Hydrogen Direct-Injection Engines Using Air Injection

hiroki sawaguchi･hidenori kosaka (Institute of Science Tokyo)

The promotion of mixing between hydrogen and air is effective for improvement of thermal efficiency of hydrogen direct injection engines. This study proposed an engine system with air direct-injection in order to improve mixing characteristics, and implemented zero-dimensional simulation to evaluate the thermal efficiency of proposed engine. Moreover, CFD analysis of hydrogen jets and air jets into a constant-volume container was conducted in order to investigate the effects of air injection to the mixture formation.

Improving Thermal Efficiency and NOx Reduction Effect of High Injection Rate in High-Output and Low-Pressure Direct-Injection Hydrogen Engines

Kentaro Minoda (Tokyo City University)･Nobuhiro Shimmura (Tokyo City University / Kawasaki Heavy Industries Ltd.)･Masakuni Oikawa･Seiya Yamada･Shota Tsukamoto (Tokyo City University)･Sekai Miyamoto (Kawasaki Heavy Industries Ltd.)･Yuji Mihara･Yasuo Takagi (Tokyo City University)

Supercharging is an effective method for increasing the output of low-pressure direct-injection hydrogen engines. However, there are concerns that it may increase NOx emissions owing to worsened mixture formation. In this study, the engine performance under high-output operation was evaluated using injectors with the same nozzle hole geometries but different injection rates. The results confirmed that employing a high-injection-rate injector improved thermal efficiency and reduced NOx generation during high-output operation.

Research on Abnormal Combustion in Hydrogen-Fueled Spark Ignition Engines (2nd Report)
-Construction of Pre-Ignition Prediction Model Caused by Hot Surface-

Hiroki KAMBE (Toyota Industries Corporation)･Ryo MASUDA (Toyota Central R&D Labs.)

The first report revealed that NO in the residual gas of Hydrogen-fueled spark ignition engines significantly reduces ignition delay time. This report presents a 1D-CFD model for predicting pre-ignition due to thermal surface ignition, incorporating the effects of NO. In experiments, spark plug temperatures were measured to investigate the mechanism of pre-ignition. Using these experimental results, in-cylinder flow and thermal source temperature were modeled, leading to the construction of the pre-ignition prediction model. The model successfully reproduced the pre-ignition phenomena observed in actual engines when advancing the ignition timing.

Study on Homogeneous Mixture Formation by High-Flow Hydrogen Jet

Seiya Nishimura･Akichika Yamaguchi･Shingo Kitani (DENSO)･Hajime Kataoka (SOKEN)

Hydrogen engines are attracting attention as a pathway toward carbon neutrality; however, achieving abnormal combustion avoidance, high output, and low NOx emissions requires overcoming the challenge of homogeneous mixture formation. This study focuses on high-flow hydrogen jets for large engines and analyzes the formation mechanism using advanced visualization techniques. Based on the identified mechanism, injection and jet requirements effective for homogeneous mixture formation were derived through CFD analysis.

A Study on Waste Heat Recovery Efficiency using Thermoelectric Devices in Hydrogen Engines

Itsuki Motomiya (Tokyo City University Engine Research Laboratory)･Satofumi Maruyama (Tokyo City University Engeneering Materials Laboratory)･Koichi Nishibe (Tokyo City University Fluid Engeneering Laboratory)･Akemi Ito (Tokyo City University Engine Research Laboratory)･Koji Kikuhara (Waseda University)･Miyuki Usui (NPR-RIKEN CORPORATION)･Ryosuke Ichimura (Tokyo City University Engine Reseach Laboratory)･Yuma Osawa (Tokyo City University Fluid Engeneering Laboratory)

Hydrogen engines tend to operate with a high air-fuel ratio to prevent abnormal combustion, resulting in lower exhaust temperatures compared to conventional engines. This enables the potential use of high-efficiency thermoelectric devices designed for low temperatures, for waste heat recovery. Temperature at various points on the exhaust system was measured using a hydrogen engine truck during actual road driving. The optimal point for installing the thermoelectric devices was investigated, and electric power generated was estimated.