This article focuses on the first-place project of the Shanghai Science and Technology Progress Award for 2022, titled "Preparation of Biodiesel from Waste Cooking Oil and Key Technologies for Automotive Applications," led by Professor Lou Diming from the Automotive Engine Design Institute at Tongji University.

On a November afternoon in 2017, truck driver Master Liu pulled into a gas station in the Fengxian District of Shanghai. He was a regular at this gas station and quickly noticed the new signage: "B5 Diesel" in white letters on a green background, with the tagline "Cheaper by 0.3 yuan/liter" underneath. Master Liu, who is quite budget-conscious, was intrigued but had some reservations, so he inquired with the staff for more details. They informed him that B5 Diesel is biodiesel, with performance comparable to regular diesel and a more environmentally friendly profile; it was just in the pilot phase of rollout, hence the lower price. Reassured, Master Liu decided to try this new fuel, and filling up a tank cost him nearly twenty yuan less than regular diesel.

After completing his deliveries, Master Liu shared this with his fellow drivers in a group chat. Most expressed interest in trying it, but some raised concerns: they had heard that B5 Diesel was made from gutter oil, and using it excessively might harm their engines—potentially negating any savings on fuel repairs.

So, what exactly is B5 Diesel? Is it really made from gutter oil? Will B5 Diesel actually damage vehicles?

B5 Diesel is a new type of fuel created by blending biodiesel (derived from animal fats, vegetable oils, and other biological oils, classified as renewable energy) with petro-diesel (derived from crude oil, classified as non-renewable) in a 1:19 ratio (meaning biodiesel comprises 5%).

Some may wonder: why mix biodiesel with traditional diesel when the latter works fine? The reasons are twofold: energy security and carbon reduction for environmental protection.

Petroleum is often referred to as the "blood of industry," vital to human society during the industrial era. However, it is a non-renewable resource that will eventually be exhausted, and its uneven distribution across the globe creates disparities—some areas are "oil-rich," while others have virtually none. This reality leads to frequent price fluctuations in the global oil market, and countries dependent on oil imports feel the pinch during geopolitical crises like the Russia-Ukraine conflict. Biodiesel does not have this issue.

Additionally, biodiesel performs just as well as petro-diesel in terms of combustion while significantly outshining it in environmental benefits. It is estimated that burning a ton of biodiesel can reduce carbon dioxide emissions by approximately two tons compared to petro-diesel. Furthermore, the harmful substances emitted (such as particulate matter and carbon monoxide) are much lower, and biodiesel provides better lubrication. In summary, biodiesel is more eco-friendly and offers a better security profile than petro-diesel.

In this context, biofuels have rapidly gained global traction; for instance, Europe established the Renewable Energy Directive (RED) in 2009, revised as RED II in 2018, mandating that the use of biofuels in ground transportation increase to 14% by 2030. As one of the largest oil-importing countries globally, China also places significant emphasis on developing biofuels. However, as a major consumer of edible oils, common raw materials for biofuels like palm oil, soybeans, and rapeseed must be heavily imported, leaving little for biofuel production. Under the principle that biodiesel shouldn't "compete with human food," waste cooking oil has become a crucial raw material for biodiesel production in China.

Strictly speaking, waste cooking oil comprises various categories, including used frying oil, leftover oil, and gutter oil, with gutter oil having the worst sanitary conditions, previously igniting public food safety scares. In the current context, gutter oil is essentially equated with waste cooking oil. The biodiesel mixed in the B5 Diesel that Master Liu used was indeed made from waste cooking oil, confirming that B5 Diesel production does utilize gutter oil. So, does B5 Diesel really harm vehicles?

Firstly, poor fuel quality can damage vehicles, and gutter oil is often associated with "dirtiness" and "smell," leading to concerns that it cannot be high-quality fuel. Such apprehensions from experienced drivers are not unfounded. However, biodiesel produced from fully refined, processed, and treated gutter oil can indeed meet the standards required for vehicle use, thanks in large part to the efforts of researchers.

As early as 2006, Professor Lou Diming's team from Tongji University worked on the national 11th Five-Year Plan 863 project titled "R&D of Biodiesel Components and Automobile Matching Technology," which successfully developed the key technologies necessary for blending biodiesel with diesel fuel to match engine specifications. This advance eliminated the need for creating dedicated engines for biodiesel, allowing drivers to simply refuel their existing diesel engines with the new biodiesel blend. Moreover, this new fuel competes economically, maintains performance, and minimizes engine wear compared to traditional petro-diesel. Consequently, the project's results, known as "Key Technologies and Applications of Diesel Fuel Blending," won the first prize in the 2012 Shanghai Science and Technology Progress Awards.

After proving biodiesel's viability in laboratory studies, in a trial from December 2013 to October 2014, 50 buses in Shanghai utilized "gutter oil diesel." The results were promising: the new diesel blended with "gutter oil" only increased fuel consumption by 1% to 3% compared to pure petro-diesel, and while maintaining vehicle power, emissions for carbon monoxide and other pollutants were lower, with particulate matter reduced by nearly 10%. Additionally, key engine components such as piston tops, valves, and fuel injectors had no carbon buildup, and no fuel system-related failures were reported. This new biodiesel met expectations for "no loss in performance and increased greenness." In 2017, B5 biodiesel officially appeared at social gas stations in Shanghai. By mid-2023, nearly 300 gas stations supplied B5 biodiesel, cumulatively providing over 1.8 million tons—on average, at least one in four diesel vehicles has used B5 biodiesel. Furthermore, at stations offering B5 biodiesel, this eco-friendly fuel accounted for over one-third of total diesel usage.

Undoubtedly, this environmentally friendly fuel derived from gutter oil has withstood the test of practice. Nowadays, drivers are no longer as skeptical about B5 diesel as they were back in 2017, with an increasing number choosing the performance-maintaining, affordable B5 biodiesel.

However, the reason B5 biodiesel can maintain its price advantage of 0.3 yuan per liter primarily stems from government subsidies. To expand its market reach further and potentially replace pure petro-diesel entirely, biodiesel needs to optimize production processes and lower costs to create genuine price competitiveness.

In this context, Lou Diming's team at Tongji University, having worked in the biodiesel field for many years, developed the "Preparation of Biodiesel from Waste Cooking Oil and Key Technologies for Automotive Applications," laying a solid technological foundation for the further industrial development of biodiesel and also winning the first prize in the 2022 Shanghai Science and Technology Progress Awards.

At this point, many readers might wonder: a barrel of crude oil costs nearly a hundred dollars, while gutter oil is almost free—why can’t the cost of biodiesel made from gutter oil be lower? While it's true that gutter oil itself is inexpensive, recycling and processing it to meet the quality standards required for biodiesel production comes at a significant cost. The core issue here is that there is a vast difference from one gutter oil source to another. Gutter oil originates from the kitchens of various restaurants, and the diversity of kitchen environments is substantial. For example, can the waste oil from a spicy hot pot compare to that from sweet and sour ribs or braised chicken? Each dish generates unique waste oil, and the resulting mixed gutter oil can vary widely. In essence, each barrel of gutter oil presents a new challenge. Moreover, as a suitable fuel for vehicles, biodiesel must have stable, uniform chemical properties that are compatible with all engines. The contradiction between the diversity of raw materials and the need for standardized products represents a "consistency" challenge in the production of biodiesel from waste cooking oil.

Chemically, the primary aspect of variability in gutter oil is the vastly fluctuating acid value. For biodiesel to be a viable product, this must be reduced to a certain standardized level; otherwise, it may corrode vehicle components. To address this, Lou Diming's team innovatively introduced nano-scale metal oxides into the reaction process to enhance the adhesive strength of the active components in the catalyst. This adaptation accommodates the significant fluctuations in acid values associated with waste cooking oil, while also improving the activity, selectivity, and lifespan of the catalyst.

Simultaneously, the team developed a full continuous, fully automated, integrated, and stepwise four-tower distillation technology to produce biodiesel from waste cooking oil. This approach allows for a high-quality, continuous automated production process through multiple stages of processing, spatial esterification, intelligent distillation, and online blending.

The four-tower distillation technology developed by Lou Diming's team

As a result, regardless of the origin of the gutter oil, the previous dish it came from, or whatever seasonings or detergents it may have mixed with, as long as it enters Lou Diming's production process and utilizes the specially formulated catalyst developed by the team, a stable and consistent quality biodiesel can be produced.

After resolving issues with the raw material, Lou Diming's team also focused on the way biodiesel engines utilize fuel.

Team member Hu Zhiyuan said: “The use of biodiesel in vehicles has flexible proportional applications. The instantaneous changes in diesel engine operating conditions lead to challenges in ‘adaptive fuel injection control, efficient combustion with varying proportions, and collaborative control of PM and NOx emissions.’”

For engines to operate efficiently, precise fuel injection and efficient combustion are key. In practice, biodiesel is typically blended with petro-diesel, with flexible mixing ratios, and coupled with rapid changes in diesel engine operating conditions, raising demands for precise injection control—hence the challenge of “adaptive fuel injection control.” To tackle this, Lou Diming's team innovatively proposed adjusting fuel injection in real-time based on the ratio of biodiesel and the operating conditions of the diesel engine, inventing a multi-model coupled adaptive fuel injection control method for biodiesel engines. This method gathers multi-source sensor signals, including fuel temperature, coolant temperature, vehicle speed, and throttle position, to perform multi-model coupling and online adjust the injection control strategy, thereby achieving timely, precise fuel injection. In simpler terms, sensors placed at various key points throughout the vehicle continuously collect essential data, which is then processed and analyzed to calculate the optimal fuel injection plan that is fed back to the relevant components for execution.

Lou Diming's team's multi-model coupled adaptive fuel injection control method

Moreover, due to the flexible mixing ratios, efficiently burning biodiesel poses additional difficulties. Team member Wang Zhong pointed out that the crux of the matter lies in "combustion mode control." As a solution, the Lou Diming team initially conducted foundational research on the combustion of flexibly proportioned biodiesel to clarify the essence of “micro-explosive breaking” and “composite flame propagation,” subsequently proposing an efficient combustion model characterized by “active pre-mixing dominance, catalytic oxygen-containing groups, multi-point ignition diffusion, and controllable turbulent combustion,” significantly improving the combustion efficiency of flexibly proportioned biodiesel.

Lou Diming's team's proposed efficient combustion mode for flexibly proportioned biodiesel

Another challenge posed by the characteristics of biodiesel and engines is the difficulty of synergistically controlling particulate matter (PM) and nitrogen oxides (NOx) emissions. Lou Diming highlighted that the core of this issue lies in the "contradiction between PM and NOx emissions," meaning that reducing PM often leads to increased NOx emissions, and vice versa. Both PM and NOx are major pollutants in automotive emissions, and minimizing both is essential to meet green environmental standards; otherwise, the environmental advantages of biodiesel could be significantly undermined.

To resolve this, Lou Diming's team proposed utilizing NO2 as a regulating medium to decouple the PM and NOx control contradictions, creating an adaptive control technology for the post-treatment system of flexibly proportioned biodiesel. This innovation enhances the adaptability of the exhaust purification systems to variations in biodiesel ratios and engine combustion conditions while also reducing PM and NOx emissions.