His research has contributed to scientists’ fundamental understanding of how fuels burn and has advanced innovation in alternative fuels and combustion technologies for cutting carbon emissions in power and propulsion systems and low-carbon techniques for chemical manufacturing. His research has led to the recent discovery of plasma and ozone assisted cool flames and warm flames. He also investigates new nano-scale materials needed for batteries and other sustainable energy systems.

Ju earned his bachelor’s degree in engineering thermophysics from China’s Tsinghua University in 1986 and his Ph.D. in mechanical and aerospace engineering from Japan’s Tohoku University in 1994. He joined the Princeton faculty as an assistant professor in 2001 and was named to the Patterson professorship in 2013. He has published more than 260 refereed journal articles and is a fellow of American Society of Mechanical Engineers and a fellow of the Combustion Institute where he serves on the board of directors. He received the 2021 Propellants and Combustion Award from the American Institute of Aeronautics and Astronautics.

Ju also has been outspoken about issues of discrimination against Asian Americans. In recognition of Asian American and Pacific Islander Heritage Month, Ju recently spoke about his path to Princeton and reflected on current challenges facing Asian Americans.

Please tell us something about your path to your current position? What were some formative moments?

I was born in very poor family, in the countryside in China. My parents were peasants. I studied five years in primary school. I had pretty good grades, probably top 10% in my class, but I didn’t have a chance to go to middle school because my father said, “I’m not a party member. I’m not some kind of leader in the countryside. Look, you may not able to make it to middle school and will have to work with me to make a living.” Indeed, my father was right. I was not recommended for the admission to middle school. I worked with my father to dig Chinese medicines from the mountains and I tried to sell to the medicine shop. One day, my father asked me – he could not read any Chinese characters – “Can you read that name to me? What is the price?” I said, “I cannot read that in Chinese letters.”

He said, “Oh, after 10 years you will be the same as me. You cannot read anything. So, can you go back to the primary school to study one more year and to remember more Chinese words and come back?” I did that. I went back to primary school to restudy in the fifth grade.

My grandmother understood that the only thing that would change my future was education. You know what she did? She quietly took the chicken eggs in our house that normally we could not afford to eat ourselves. We normally brought them to market for money. She kept sending the eggs to a party leader of my village without us knowing. When I tried to see whether I had the opportunity to move to middle school, the party leader said, “He’s good. So why not? Just let him go to middle school.”

I was the number one student in middle school but I didn’t have the money to buy the ticket to take the general exam for high school. My teachers just gave me the money to take the test in the capital of the county.

In 1976, Chairman Mao passed away. The new Chinese leader Deng Xiaoping said, “We’ve got to restore our education.” Then we started to understand the best students could have a chance to college. Luckily, I went to the best university of China for my college. Later, I got my Ph.D. in Japan and became a faculty member for five years at Tohoku University. Then I went back to Beijing and took a faculty position at Tsinghua for one year in 2000.

During that one year, I feel that China gave us a great platform to do research, and a lot of resources. Nevertheless, I think that the most important thing is academic freedom, which I think that China didn’t have at that time. I thought America is a wonderful place for research, and the top of the pyramid in my research area was Princeton. The combustion research group is the “hometown” for combustion research – anywhere you go, all the top researchers are related to Princeton, either studying here or being a postdoc. So that is how I arrived at Princeton

What sparked your interest in combustion engineering?

Combustion is so beautiful because the flame itself is so beautiful. If you look at the candle light, if you look at rockets, if you look at aircraft and internal combustion engines – they power the world. For mankind, fire is what makes humans different from other animals because we mastered the knowledge of how to use fire, how to make food, how to power engines… and how to celebrate birthdays. This is the romance of using fire. It’s so fascinating.

And particularly for me, I’m interested in combustion because of aerospace. Aerospace is a history of innovation, making new systems that never existed and a vehicle for exploration of space and other planets.

Has your Asian heritage presented barriers during your career?

As an Asian, the language can become a big problem, particularly for me. When I came here, I could barely speak English. Sometimes when a student raised a question, I was not able to understand the question. So I was very depressed for the first couple years. I talked to the department chair at the time, Lex Smits. He said, “Okay. We are going to measure you by your scholarship. Don’t worry about the language barriers. You will get better and I believe you.” That was a huge support to me. Princeton is really a tolerant space to scholars.

If there was something that you could clarify about people’s perceptions of Asian Americans in STEM, what would it be?

People have the perception, “You are an Asian guy, so you are good at math.” That’s what I heard from a professor here. He said, “Oh, you Chinese people, your brain is born different with math brain.” I think that is a wrong conception. I think the reason that Asian kids may be particularly good at STEM and math is because of their culture, the focus of their parents. The parents had to make a lot of sacrifice in terms of time, in terms of money. They probably do not live in a better house and cancel their travel and they eat maybe simple food to save money for education. It’s not because their talent is more. I think it’s because they spend a lot of time, and effort, and the resources on it.

Another misperception is that people with Chinese heritage may not be loyal Americans. The China Initiative [a U.S. Department of Justice effort to combat espionage] presents a lot of threat to us. They are targeting us, and they say now that we are maybe spies of China. We are not. Just because you came from China, then you become targeted. Any mistake in your report could be evidence or be prosecuted. This is rather sad today. Because I am of Chinese origin, because I might have studied in Asia and I taught at a University in Asia, then I become racially profiled. I’m hesitating to apply any kind of Department of Defense or NASA grant, which have been supporting me for many, many years, because of the China Initiative.

I think America is really great country. It has provided us a lot of opportunities, particularly that of equality and freedom. For example, I was able to get my first research grant from the Air Force and NASA, even though I was not yet an American citizen. I was really surprised, and I felt very appreciated.

I was also selected around 2010 to serve on a NASA Rocket Committee to understand what we should do in the future in terms of space propulsion. George Bush had made a decision, and Obama also, to cancel the Space Shuttle Program. America didn’t have a rocket that could send anybody or even equipment to the International Space Station. America lost any kind of capability doing space exploration. That was so depressing at the time. With the committee, we spent about a year visiting all NASA centers try to define what will be the future for America’s rockets – to make America a comeback kid again.

The committee made a great decision to welcome industry to compete, to commercialize the space launching system. We recommended Congress to fund commercial companies to join space exploration efforts, particularly at the lower Earth orbit. That policy is what made Space X successful, and made America so exciting today. The innovation came.

That is so exciting for me, to witness that history of the United States – that frustration and then the glory of space propulsion. It’s so interesting. I think that this is a great example of America’s opportunity. But today, that you can see a difference.

I never questioned my loyalty to America. I think I made a contribution to the rocket policy at least by serving in national science committees, in addition to contributions to my technical area. I think America right now is really at a crossroads, whether we really respect science or not to make America the leader in the world. Science supports the economy and the things to support science are the quality of education and the talent of immigrants. That’s what I always believe.

What would you say now to a young person starting in your field? Where are the interesting opportunities?

One opportunity is in space propulsion. How do you make rockets that are efficient or reusable to go to Mars and beyond? How do you make fuel, convert the CO2, on the Mars surface into the fuel to allow the rocket to fly back?

The second thing I would say that there’s huge opportunity in low-carbon energy conversion. Today more 80% of our combustion of fossil fuels is harming the future due to carbon emissions. Going forward, power generation will be shifted to hydrogen and ammonia as energy carriers. So the question then is how do you generate advanced gas turbines that can burn hydrogen and ammonia for energy conversion? At the same time, how do you convert the abundant methane, the petroleum, and biomass into hydrogen and valued carbon materials using the knowledge of combustion?

Lastly, I think the kind of culture that focuses on education and family is so important. My parents and my grandma knew that the only thing to change you, particularly if you are at the bottom of society, is education. So no matter how poor you are, study hard and find the opportunity for yourself. That’s the only thing. If you are at the bottom, that’s the only thing to change your life.