Picking Up Speed

Hybrid engines and other new technologies are making rapid advances in controlling automotive emissions and improving fuel efficiency

Nearly four decades ago, a dramatic deterioration of air quality and repeat occurrences of smog in large cities such as New York and Los Angeles led to national recognition of the growing problem of pollution from the automotive sector. As a result, Congress passed the Clean Air Act of 1970 – the first major environmental law intended to improve air quality by reducing emissions and pollutants from their sources. A key aspect of this legislation was the identification of “criteria pollutants,” specific constituents of air pollution such as ozone, sulfur oxides, nitrogen oxides and carbon monoxide, which would be monitored and controlled via additional regulations.

Additional Cost ($) Reduction in CO2 (%) Purchase payback period (years)
Advanced gasoline direct injection 742 24 3
Diesel 1141 24 3
Advanced Diesel Engines 469 18 2
Gasoline Hybrid 3186 48 7
Diesel Hybrid >3000 >50 >7

Emissions Reduction Progress
During the past few decades, the automotive industry has made tremendous advances in reducing pollutants in auto emissions. In some cases, such as the reduction of diesel particulate emissions in Europe, the industry voluntarily introduced new and clean technologies, but, in other cases, progress is largely a result of aggressive legislation. For example, the tailpipe emissions of hydrocarbons from gasoline cars were reduced from 10.6 gallons per mile (g/mile) in 1971 to 0.06 g/mile by 2004. In addition, smogproducing NOx was reduced from 3.6 g/mile to 0.05 g/mile.

Despite those reductions, the rapid growth in car sales around the world, especially in countries with developing economies such as China and India, has increased the need for a continued decrease in automotive emissions. Additionally, now that the link between carbon dioxide emissions and global warming is firmly established (See Figure C), it has become imperative to innovate around technologies that reduce emissions and improve fuel economy simultaneously. With or without pressure from global treaties to curb greenhouse gas emissions, e.g. the Kyoto protocol, the automotive industry is positioned to accept and meet these challenges.

In order to reduce tailpipe emissions of carbon monoxide and un-burnt hydrocarbon vapors, catalytic converters were introduced in the United States on all new gasoline cars in 1980. Between 1980 and 1993, on-board diagnostic controls and three-way catalytic converters were also introduced. The new solutions used finely dispersed platinum, palladium and rhodium as catalysts on ceramic honeycomb substrates and simultaneously reduced carbon monoxide, hydrocarbons and nitrogen oxides in the tailpipes. Threeway converters remain the norm in gasoline vehicles, although, refinements in electronic controls and material chemistries have improved their performance several-fold.

It is unfortunate that while toxic gas emissions from gasoline engines decreased dramatically over the past few decades, the average fuel economy of our cars has not improved and still lags significantly behind competitor economies in Europe and Asia. For example, while the U.S. corporate average fuel economy (CAFE) hovers around 25 miles per gallon (mpg), Europe has crossed 40 mpg limits. Japan is already approaching 53 mpg. Similarly, while there are only two car models on sale in the United States that average over 40 mpg, there are over 113 such models available for sale in Europe. In a world where fuel economy improvements are linked directly to global warming and climate change, it is a shame that the United States has not made much progress. The U.S. automotive industry appears to have realized the challenge at last and is introducing more pro-environmental technologies. Some advanced engines today have very low emissions and also provide high fuel economy. Examples include advanced gasoline, gasoline hybrid, diesel and diesel hybrid, plug-in hybrid and, in the future, hydrogen fuel cell vehicles.

Fuel Alternatives on the Rise
While plug-in hybrids and fuel cell vehicles are still some years away from commercialization, high fuel economy

Holy Grail Technology: Hydrogen Fuel Cells

The most significant shift in the energy source that will propel fuel-efficient car manufacturing will happen when hydrogen fuel cell vehicles become widely available. However, the industry must overcome major technological barriers before commercial use of fuel cells can become reality. Despite being a common element, pure hydrogen gas is rare and has to be isolated, compressed, transported and stored, requiring a large amount of energy from other sources such as fossil fuels.

Some experts argue that automakers can reduce carbon dioxide emissions by a greater degree by improving gasoline and diesel engines – rather than by shifting to hydrogen fuel cell vehicles. This may be true, but innovations in materials science, especially the use of novel hydrogen storage materials, could change that equation in the future.

alternatives are already available. Nextgeneration gasoline vehicles (e.g. VolkswagenW Jetta GDi), gasoline-hybrid vehicles (e.g. Toyota Prius+, Ford Escape SUV) and diesel vehicles (e.g. Mercedes SClass, Honda Accord diesel) are either already available or will be available as early as 2008. While the industry continues to debate which technology platform will be most successful commercially, the ultimate decision will be made by the consumer. In the absence of tightening CAFÉ standards (several bills have been introduced in the U.S. House of Representatives), it is hoped that people will demand more fuel-efficient vehicles and continue the momentum started by more progressive states such as California, where the state is mandating a limit on automotive greenhouse GHG emissions.

The California Air Resources Board (CARB) estimates that adoption of advanced technologies (non-hybrid) can lead to 18-24 percent improvement in carbon dioxide emissions from the automotive sector. However, the economics are quite different for each technology platform, and this is where consumers will make choices based on price, performance, durability and driving experience. Table 1 provides an estimated comparison of cost and carbon dioxide emission reduction for five competing technologies.

Along with advanced gasoline direct injection, diesels and diesel hybrids stand out as promising choices for meeting our near-term mobility needs. During the past decade, diesel engines have made dramatic improvements in performance, acceleration, fuel efficiency, emissions and noise. Even companies that first introduced gasoline electric hybrids now plan to introduce “clean diesels” in markets around the world. For example, Honda has announced plans to introduce diesel cars in the United States that will offer more than 62 mpg. Given the superior performance of clean diesel vehicles coupled with lower taxes on diesel fuel, more than 50 percent of all new cars sold in Europe are diesel.

Modern-day clean diesels utilize progressive emission control systems that complement advances made in combustion processes, fuel injectors and electronic controls. The introduction of advanced, high-porosity ceramic diesel particulate filters (DPFs – see Figures E1 and E2) and novel catalyst systems has made this task not only possible but also affordable. Also, the quest for advancing highly fuel-efficient clean diesels has prompted rapid and breakthrough innovations in materials and ceramic sciences, catalyst chemistry and electronic systems integration. Innovative small firms and established auto companies are working hard to make clean diesel and diesel-electric hybrids an economically viable reality in the near term. The task to achieve greater than 100 mpg fuel economy is clear and doable in the near future.

Automotive Emissions’ Impacts

Internal combustion engines used in both on-road and off-road applications, including cars, trucks, boats and construction equipment, are significant contributors to air pollution. These engines emit carbon monoxide, volatile organic gases, nitrogen oxides, soot and carbon dioxide, and lead indirectly to the formation of toxins such as ozone in the atmosphere. Epidemiological studies conducted across the country have now identified direct links between exposure to these toxins and adverse health effects such as asthma and bronchitis, as well as cardiovascular, pulmonary and lung diseases. In addition, gaseous and particulate toxic pollutants in breathable air cause nasal irritation, asthmatic episodes and long-term tissue damage. Inhalation of fine particulate matter (soot) can also lead to bronchial problems and scar tissue formation deep inside the lungs. Finally, greenhouse gas emissions from the automotive sector influence global phenomena such as abrupt climate change, reduction in crop harvests and increased occurrence of acid rain.


More Fuel Choices on the Horizon
While clean-diesel vehicles are the best-in-class choice to solve the automotive emissions problem of today, there is certainly a need to develop technologies that will lead to further advancements over the longer term. Recently, some innovators have focused on the use of bio-fuels — particularly corn-based ethanol fuels. Ethanol-fueled vehicles have lower toxic emissions per unit distance traveled but provide lower fuel economy (mpg) than current gasoline engine vehicles. While there is a case to be made for reducing energy dependence on imported oil, the positive environmental impact and the negative impact on food prices due to widespread use of ethanol as fuel is still in question.

Despite the viable solutions on the horizon – diesel hybrids, fuel cell vehicles, etc. – and the tremendous innovation already achieved, automakers must challenge themselves to innovate at the next level. Current fuel-efficiency standards and increases in global warming underscore a need for newer technologies that not only reduce emissions from the tailpipe but also convince consumers to make a conscious shift toward adopting more fuelefficient automobiles. Continued innovation and an overall reduction of CO2 emissions from the transportation sector are not only the most responsible courses of action, but also opportunities for the automakers to reinvent themselves as the vanguards of clean transportation and a cleaner environment.

This article originally appeared in the 11/01/2007 issue of Environmental Protection.

About the Author

Dr. Bilal Zuberi is a co-founder and the vice president of product development for GEO2 Technologies, a Boston-based materials science technology development firm with a special focus on emissions reduction from internal combustion engines. Dr. Zuberi holds a PhD in physical chemistry from the Massachusetts Institute of Technology (MIT), where he worked on microphysics of atmospheric emissions such as soot particles, heterogeneous atmospheric chemistry, and urban air pollution, especially pollution in mega-cities, under Professor. Mario J. Molina (Chemistry Nobel Laureate, 1995). He is an author of several peer-reviewed publications and U.S. patents in the area of atmospheric chemistry, materials science, and automotive emissions reduction. Dr. Zuberi can be reached by phone at (781) 721-6306.

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