The application of hydrogen energy in automobiles is mainly through fuel cells, but there is no shortage of technical routes such as the hydrogen internal combustion engine, which has the same principle as the fuel internal combustion engine, on the market. The hydrogen fuel cell is an advanced and efficient energy conversion device that converts the chemical energy of fuel into electrical energy directly through a chemical reaction without combustion. In contrast, the hydrogen internal combustion engine is a kind of power equipment that releases the chemical energy of the reaction gas through combustion and does work through gas expansion, and the energy conversion efficiency is limited by the Carnot cycle, and the fuel utilization rate generally cannot exceed that of the hydrogen fuel cell.
Schematic Diagram of Hydrogen Internal Combustion Engine
Data Source: Public Information
In 2021, Toyota is making a lot of moves on hydrogen internal combustion engines, once again creating an industry buzz about hydrogen internal combustion engines. In April 2021, Toyota announced that it is developing hydrogen internal combustion engines to promote a carbon-neutral society.In September 2021, Toyota announced that it would release two models with hydrogen internal combustion engines, the Prius and Corolla, by the end of 2022. In December 2021, Toyota showed a prototype Toyota GR Yaris H with a 3-cylinder 1.6T displacement hydrogen internal combustion engine.
Hydrogen Internal Combustion Engine Prototype Toyota GR Yaris H
Data Source: Public Information
The hydrogen internal combustion engine is not a new technology. As early as 1979, BMW Motor Group developed the first hydrogen internal combustion engine car and launched several series of hydrogen internal combustion engine cars in subsequent years. In 2000, BMW Group's BMW 745h model was unveiled at the Frankfurt Motor Show in Germany. In 2004, the BMW H2R hydrogen internal combustion engine concept race car based on the BMW 760i 6.0L V12 gasoline engine was officially released, equipped with a 6.0L V12 engine with a maximum power of 210kW, driving a body of 1.5 tons and reaching a top speed of 300.175 km/h, completing the test at the French high-speed test track and setting up to 9 speed records, fully demonstrating the huge potential of hydrogen internal combustion engine cars. In 2007, BMW released the world's first hydrogen-powered car "BMW Hydrogen 7 Series", with a 191 kW/260 hp 6.0L V12 engine, maximum power 191 kW, maximum torque 390 N-m, running from 0 to 100 km/h in 9.5 seconds, with a top speed electronically limited to 230 km/h. If the adequate supply of hydrogen is not guaranteed, this V12 engine can quickly switch to conventional gasoline working mode. In 2019, BMW unveiled the i Hydrogen Next with hydrogen fuel cell technology converting an X5 model to a hydrogen fuel cell that holds two 70MPa hydrogen tanks capable of holding 6 kg of hydrogen. The hydrogen fuel cell system produces about 125kW of power generation and 275kW of motor output.
BMW Hydrogen 7 Series Hydrogen Internal Combustion Engine Automobile
Data Source: Public Information
BMW i Hydrogen Next
Data Source: Public Information
Hydrogen internal combustion engine is similar to fuel internal combustion engine in structure, but it has been delayed to enter the market, the primary reason is that its technical difficulty is much higher than that of fuel internal combustion engine, and it has to overcome three technical difficulties of early combustion, deflagration and tempering, and it is still in the R&D stage, and its technical maturity is not as good as that of hydrogen fuel cell.
Hydrogen Internal Combustion Engine Technical Difficulty Table
|
Name |
Characteristics and Hazards |
|
Early combustion |
After the intake valve is closed in the hydrogen internal combustion engine, when not ignited by the spark plug, the fresh charge contacts with some hot spots of high local temperature in the combustion chamber causing a mixture of fuel gas burning in the cylinder. The hot spots include spark plugs, exhaust valves, carbon deposits, high-temperature wall and its angles, etc. |
|
Deflagration |
Deflagration refers to the spontaneous combustion of the final combustion mixture in the hydrogen internal combustion engine after the completion of ignition, far from the flame, before the flame front surface has not reached the combustion. It is a kind of abnormal combustion, mainly manifested as the cylinder pressure for high-frequency large fluctuations, the engine vibration increased. And the flame spreads outward at a speed several times higher than normal combustion, resulting in a sharp knocking sound to produce the commonly known as "cylinder knocking". |
|
Tempering |
An abnormal combustion phenomenon in the process of intake of hydrogen internal combustion engine, the intake valve is not closed, the spark plug has not yet ignited the cylinder mixture and is ignited by the hot spot resulting in flame propagation into the intake pipe. "Backfire" causes the hydrogen engine to work improperly, the power drops and the economy becomes bad. Severe backfires cause high temperatures and pressures in the intake tube, resulting in a fresh charge not entering the cylinder. A hydrogen engine misfire can sometimes even damage the hydrogen supply system, causing serious accidents. |
Data Source: Public Information
Secondly, hydrogen has a very low density and requires a very large amount of space under the conditions of its presence as a gas. According to the study, when entering the cylinder under the same conditions, hydrogen takes up about 15~30 times more cylinder gas than gasoline, so it will lead to a decrease in efficiency.
Again, the fuel utilization rate of hydrogen engine is not high, which is commonly known as hydrogen is not durable. At that time, the hydrogen consumption of BMW Hydrogen 7 series hydrogen internal combustion engine car launched by BMW in 2007 was 3.7kg/100km, while the fuel cell passenger car was usually 1~1.5kg/100km. Toyota's latest second-generation Mirai has a total hydrogen refueling capacity of 5.6kg and a range of 650km, which equals to less than 1kg/100km.
In addition, nitrogen gas in the air will generate nitrogen oxides to pollute the environment under the high temperature and high pressure working environment, which cannot achieve 100% environmental protection of hydrogen fuel cell.
Finally, hydrogen gas can cause hydrogen embrittlement of metals, which affects the safety performance of the engine.
The biggest advantage of hydrogen engines over hydrogen fuel cells is the cost. Currently, a 100kW hydrogen fuel cell system costs about 500,000 yuan (prototype), and a domestic diesel engine sells for about 60,000 yuan for 100kW, while the cost of a hydrogen internal combustion engine is about 15% more expensive, at about 69,000 yuan.
