Diesel Engines: United States and Europe
Diesel engines are routinely sold in European automobiles, with an estimated 6. 5 million vehicles on the road as of 2003 (DeGaspari 28). In both Europe and the United States, diesel engines are used in industrial and commercial applications like generators and commercial vehicles.
However, the United States has historically been slow to embrace the concept of a diesel-powered personal automobile, and diesel automobile engines are only recently beginning to gain any traction in the US auto market. What are the reasons for this reluctance, and how can diesel engines gain more of a market share?
The reasons for US market slowness in adopting diesel engines are varied. First, the diesel engine suffers from a perception problem which dates to the engines of the 1960s and 1970s – Americans believe that diesel engines are dirty, inefficient and noisy, making for an uncomforta-ble passenger ride, higher emissions and an insufficiently powerful engine. Second, diesel engines cost more than traditional gasoline-powered engines; with American gas prices being historically much lower than European gas prices, there has been no financial incentive in the past for the adoption of diesel engines in the United States.
Third, the availability of diesel fuel is not con-sistent across the United States and it is often more expensive than gasoline. These issues are being addressed in a number of ways. The availability of biodiesel (diesel fuel produced from non-petroleum sources, including plant matter, byproducts from meat pro-cessing such as rendered fat and discarded cooking oil) has been increasing steadily, bringing down the price of diesel and offering an environmentally friendly alternative, while the price of gasoline has been increasing.
Newer engine designs are quiet and clean thanks to the develop-ment of fuel injection systems, with emissions as low or lower than gasoline engines. The diesel engine offers a higher mileage per gallon and a longer range (distance travelled on a tank of fuel), along with a higher torque with a smaller engine, making them attractive choices for American sport utility vehicles and light trucks, as well as the compact car market, where consumers tend to be more conscious of energy efficiency. Historically, American vehicles with diesel engines were dirty and noisy (Siuru 52).
The high level of emissions and uncomfortable, noisy ride made a diesel engine an unattractive pro-spect, and relegated the diesel engine to commercial vehicles and applications like generators. In the late 1980s and early 1990s, however, European car manufacturers began to engage in serious research aimed at improving the technical design of the diesel engine used in passenger vehicles. At that time, the market share of the diesel engine in Europe ranged from 10% in Germany up to 35% in France, significantly higher than America, where most diesel vehicles were imported by European automobile enthusiasts (Siuru 52).
The first major improvement was introduction of an electronic fuel injection control system (Siuru 52). This system maintains an even fuel supply, reducing the loud banging noise associated with a diesel engine; it also reduces the fuel supply variation, eliminating the vibration and “hum” of a diesel automobile (Siuru 52). The first electronic fuel injection systems were indirect injec-tion systems (IDI), which mixed the fuel with air in a turbulence chamber before injecting it into the engine’s combustion chamber (Siuru 52). These engines were efficient and produced low emissions.
However, direct injection (DI), which injects the fuel directly into the engine’s combustion chamber, bypassing the admixture with air, offered even greater fuel efficiency, albeit with high-er emissions levels (Siuru 56). The direct injection system was developed by Fiat in the mid-1990s and quickly became popular (Siuru 56), The most common implementation of the direct injection system is the common rail direct injection system (Ashley 58). This system, implement-ed by most European car manufacturers in the 1998 model year, offered a way to decrease fuel consumption and emissions by about 30% from the previous designs (Ashley 58).
The common rail system uses a manifold to pre-load fuel as a buffer between the injectors and the engine, of-fering greater control of fuel usage according to driving conditions (Ashley 59). While electronic fuel injection systems improved the regularity and smoothness of the die-sel engine’s operation, particulate and nitrogen oxide (NOx) emissions were still a problem, and continue to be a problem as emissions controls for passenger vehicles become more and more tight.
While an indirect injection engine offered lower emissions due to more efficient use of fuel, direct injection engines offered markedly better performance (Ashley 57). A further challenge is that while European emissions standards are primarily concerned with carbon monoxide and carbon dioxide, American emissions standards are mostly concerned with nitrogen oxide and particulate emissions (Marshall 27). An engine which will be used in both American and European vehicles must control both adequately to meet emissions standards. Emissions are controlled in a variety of ways in the diesel-powered vehicle.
The catalytic con-verters typically used in gasoline engines don’t work with diesel engines, due to a difference in the amount of oxygen present in the engine’s combustion chamber(DeGaspari 30 ). One approach to reducing nitrogen oxide emissions in a diesel engine is to use a chemical reaction called selec-tive catalytic reaction, which uses urea (ammonia) to remove the available oxygen (DeGaspari 30). A second method, called a lean NOx trap, causes the engine to cycle between an oxygen-lean and an oxygen rich environment on a regular basis in order to “break up” the nitrogen oxide molecules (DeGaspari, 30).
These traps are often mounted to the tailpipe rather than directly in the engine (DeGaspari 30). The most common solution for particulate emissions is a filter on the tailpipe which traps particulate matter in the exhaust rather than releasing it (DeGaspari 30). The most recent advance in emissions, called homogenous charge compression ignition or HCCI, is a whole-vehicle solution to the mileage-emissions tradeoff with both gasoline and die-sel engines. HCCI, still in development, is being viewed by automobile manufacturers as a boon for the future for both gasoline and diesel engines.
HCCI uses a combination of gasoline and die-sel engine design aspects for a high-efficiency, clean-burning engine which is designed to pass emissions standards testing in both the United States and Europe (Marshall 27). The HCCI en-gine premixes air and fuel before feeding it to the engine (a gasoline engine trait), but it uses compression ignition rather than spark-plug ignition (a diesel engine trait) (Marshall 27). This en-gine has the additional advantage of being dual-fuel – it can be used with either diesel or gaso-line, reducing the pressure of fuel availability for owners of vehicles (Marshall 28).
The HCCI engine design also has the potential to be used with other forms of liquid fuel, such as hydrogen, ethanol or other forms of fatty-acid fuels like diesel and gasoline, widening the possi-bilities for alternative fuels of the future (Marshall 28). The final improvement in diesel emissions is not in the engine itself, but in the chemical makeup of the fuel. Ultra-low sulfur fuels, which were mandated by the FDA in 2006, both reduce emissions and allow for more advanced emis-sions control systems, which can be unusable with higher-sulfur fuels because the sulfur interferes with the necessary chemical reactions.
(DeGaspari 30). Engine power is another significant beneficiary of European manufacturer’s research over the last 20 years. American diesel engines have had the reputation of not being very powerful; however, the modern diesel engine has greater torque and a greater range (number of miles trav-elled on a single tank of fuel), as well as higher mileage, in a smaller, lighter-weight engine than the equivalent gas engine (DeGaspari 28). A diesel engine in a sport utility vehicle can offer forty to fifty percent greater fuel efficiency over a gasoline engine (DeGaspari 28).
The diesel version of the 2006 Jeep Liberty, which was designed with a 2. 8 liter engine, offered 27 MPG high-way/21 MPG city. Compared to its gasoline powered sibling (21 MPG highway/17 MPG city) this was a 24-30% increase in engine efficiency (DeGaspari 28). Because American cars tend to be larger than European cars, engine redesign for greater torque has been popular with American automobile manufacturers (DeGaspari 28). Diesel engines can cost significantly more than traditional gasoline engines.
The engine it-self is more expensive, as it is heavier and more precisely controlled; diesel emissions devices are also more expensive than their gasoline counterparts. A diesel engine can add one to two thou-sand dollars to the overall consumer price of a vehicle, making it unattractive if fuel efficiency is not a concern (DeGaspari 30). This problem has been self-correcting with a persistent rise in fuel costs and operational cost of automobile ownership in the United States.
In 1992, with fuel costs two to four times higher in Europe than in America, diesel engines already held a significant por-tion of the automobile market share; however, doubt was expressed that they would be accepted in America (Siuru 58). With a significant rise in fuel costs over the last 15 years, diesel has be-come more and more attractive to Americans concerned with the mileage of their vehicles. By 1997, experts acknowledged that there is an American market for diesel SUVs (Ashley 62) and currently, both European and American automobile manufacturers now offer passenger vehicles for sale in America (DeGaspari 28).
The availability and continued supply of diesel fuel is a serious concern in the United States. Europe, where as much as half the vehicles on the road at any one time are powered by diesel, took the approach of producing its own biodiesel rather than relying on imported petro-diesel (Schmidt 86). Europe has a significant percentage of arable land devoted to rapeseed (can-ola) which is primarily used in the production of biodiesel (Schmidt 86).
Biodiesel is diesel oil produced using plants or animal remains rather than petrochemicals; there are many common sources of biodiesel, including virgin plant material (canola, soy, wheat, barley, palm, pine trees, corn and algae have all been used to produce biodiesel), and used cook-ing oil from restaurants, known as yellow grease (Schmidt 86). Most United States biodiesel is derived from soybeans, which offer an 18-20% oil yield. The remaining mass can be used to pro-duce animal feed. Soybean based biodiesel releases about 3.
2 times the amount of energy used to produce it, making it an extremely efficient energy source (Schmidt 87). Biodiesel is not only good as an alternate fuel source to petroleum-based diesel, it is a cleaner fuel. According to the National Renewable Energy Laboratory (NREL), B20 biodiesel (a mixture of 20% biodiesel and 80% petrodiesel) releases l0% less carbon monoxide, particulates and total hydrocarbon, and is carbon dioxide-neutral (Schmidt 89). There are some concerns about the lev-el of nitrogen oxide emissions with biodiesel.
A 2006 FDA literature review concluded that B20 biodiesel nitrogen oxide emissions are about 2% higher than the equivalent petrodiesel (Schmidt 90). However, Scott Gordon, founder of Green Technologies, points out that catalytic convert-ers can be used with ultra-low sulfur fuels in addition to traditional emissions controls, which has the potential to greatly decrease nitrogen oxide emissions (Schmidt 90). There are a number of problems with biodiesel which are being addressed by manufactur-ers.
The first is that of agricultural resource allocation to biodiesel production. Currently, most United States production of biodiesel uses surplus soybean crops (Schmidt 86). Soybeans have a relatively low yield of only 18-20% oil, however, making soybean cultivation to meet expanded biodiesel requirements problematic (Schmidt 91). In order to expand biodiesel production, dif-ferent crops are required. Two alternatives are rapeseed (canola) and algae. Rapeseed is common-ly grown in Europe as a biodiesel source.
It has a 40% yield of oil and is easily cultivated (Schmidt 91). Algae has a remarkably high 50% yield and a production of 8,000 gallons per acre per year, making it the most productive crop found so far. However, problems with designing a large-scale agricultural system for algae have held back use of this material so far (Schmidt 91). In order to grow algae for commercial biodiesel use, indoor systems would need to be designed to precisely control growing conditions and species in tanks.
As Schmidt notes, there is the pos-sibility of creating a large supply of algae by feeding with wastewater treatment plants. Solving the technical problems of cultivating algae is essential for the continued growth of biodiesel. It is estimated that 15,000 square miles of algae cultivation (approximately 9. 5 million acres, a frac-tion of a percent of current American land given over to agricultural usage) could be enough to replace the entire stock of petroleum used in American transportation (Schmidt 91).
Unfortunate-ly, not all countries have the availability of arable land that the United States does, and environ-mental degradation can result from planting what is seen as a cash crop at the expense of sub-sistence crops or native habitat. Rain forest clearing in order to plant palm trees, a common source of imported biodiesel, has had a bad effect on Indonesian forests (Schmidt 92). A second problem with biodiesel is inconsistent low-temperature operation. All diesel fuels will gel with extreme cold, but biodiesel gels more quickly at higher temperatures.
To operate a diesel engine in colder conditions, a mixture of petrodiesel and biodiesel is required (Schmidt 89). The most common blend of petrodiesel and biodiesel is called B20 (20% biodiesel and 80% petrodiesel); however, even lower blends of biodiesel, such as B2 and B5, are beginning to gain traction in the market (Schmidt 89). A third problem with biodiesel is inconsistent quality. Federal and state tax credits for bio-diesel production make it attractive to companies large and small (Schmidt 90).
A biodiesel blend made from virgin vegetable oil is eligible for a 1-cent per gallon discount on federal fuel excise tax for each percent of biodiesel in the blend; a blend made from yellow grease, or recycled cooking oil, is eligible for half that (Schmidt 90). This is a powerful incentive for biodiesel pro-duction. Unfortunately, quality sometimes is lacking in the production controls. High levels of glycerin, a byproduct of biodiesel production which can clog filters and reduce engine perfor-mance, making it difficult to start the engine when cold, were found in one third of the samples tested by NREL in 2006 (Schmidt 90).
These samples came from blending facilities where the biodiesel fuels were mixed and then sent to distributers. The NREL attributes these problems to a sudden increase in demand leading to some plants starting production without quality control procedures in place (Schmidt 90). As gasoline prices continue to rise and the American public gives serious attention to the energy efficiency and mileage per gallon of their personal automobiles, diesel engines become more attractive to car buyers.
With fuel efficiency 30% or more higher than gasoline engines, electronic fuel injection offering a smoother, quieter ride, as well as greater torque in a smaller engine allowing for lighter-weight and higher-mileage sport utility vehicles, and the availability of biodiesel offering an environmentally friendly, renewable fuel source, the performance prob-lems of past generations of American diesel vehicles have been largely solved.
Rapid develop-ment and improvement of diesel technology to keep up with tightening emissions control re-quirements has led to extraordinarily clean vehicles. American and European automobile manu-facturers have begun to produce diesel automobiles for the American market, and have expecta-tions of solid sales. The question remains, however: will American consumers follow the lead of Europe and embrace diesel engine technology?