MAJOR FUEL ECONOMY AND PERFORMANCE IMPROVEMENTUSING ETHANOL BOOSTING SYSTEMS (EBS) TECHNOLOGY
Heightened concerns about energy security and global warming along with increased customer interest in high fuel economy point to the need for an enhanced set of options for affordable, clean, high efficiency engines. Affordability is a key issue in obtaining mass market penetration and the prospect of more stringent future emissions standards require that these options be extremely low polluting. Use of Ethanol Boosting Systems (EBS) technology in turbo gasoline engines could provide a major addition to the set of high fuel efficiency options being intensively developed today by auto manufacturers around the globe, particularly because of its cost effectiveness.
EBS technology offers a much more affordable approach than either the clean diesel or gasoline/electric hybrid propulsion technologies that are now in intensive development and production. The advantage is particularly strong for light duty trucks and other vehicles that utilize high torque, high horsepower engines. EBS technology would be much more attractive to consumers because of the lower upfront incremental cost -- less than one third of the diesel or hybrid options -- and a much shorter payback time (approximately 3 years versus 10 years, at present US gasoline prices).
EBS enhancement of gasoline engines also offers a lower cost and cleaner replacement for diesel engines in certain vocational uses of heavy duty vehicles (class 3 through 8 trucks). This advantage is primarily due to the complexity and cost of diesel emission controls required to meet increasingly stringent regulations. The EBS technology is particularly suitable for urban buses, trash collection trucks, waste haulers, cement mixers and other such equipment that is used in urban or short haul applications. Even as expensive new diesel exhaust treatment technology is deployed in these vehicles, EBS technology can provide a means to further reduce their emissions since EBS gasoline engines utilize the highly effective and proven 3-way catalytic converter for emissions control.
EBS technology makes it possible to realize the full potential of gasoline engines by utilizing the special performance enhancing properties of ethanol in conjunction with recent advances in direct injection (DI) and turbocharging. It builds on the growing interest and availability of ethanol (although methanol would be even more effective). The EBS approach uses controlled direct ethanol injection to add a very significant vaporization-enhanced On-Demand Octane BoostTM that essentially removes the knock limit on engine performance. The elimination of the knock constraint has been proven by systematic engine dynamometer tests. This allows a small gasoline engine to provide the same or higher torque as compared to a conventional engine of much larger size.
This downsizing, combined with the use of high compression ratio, enables gasoline engine operation with 25% to 30% greater efficiency in typical city-highway driving. The ethanol can be in the form of E85. The EBS technology is an innovative extension of gasoline turbocharged direct injection technology (GTDI) that is now emerging in production vehicles. It requires no inventions and makes use of the highly effective 3-way catalytic converter for emissions control. It also reduces engine weight relative to conventional naturally aspirated engines, allowing for both a direct reduction in vehicle weight and secondary reductions in chassis components such as suspension.
An immediate large market application of EBS technology is to provide octane boosting that greatly enhances the capability of gasoline engines. This is feasible with the on-demand addition of ethanol as a secondary fuel. The ethanol is stored in a separate fuel compartment from the gasoline and is used only when needed to prevent engine knock at high torque. The large evaporative cylinder charge cooling of directly injected ethanol provides a knock suppression effect that is equivalent to gasoline with an octane rating of more than 150.
With appropriate control, typical ethanol use can be limited to 5% or less of gasoline use in first generation EBS systems and 3% or less in advanced systems. With this small requirement, the ethanol tank refill could occur as infrequently as once every 4 to 6 months. If E85 pumps are not available, refill could be done at the dealer at the time of regular servicing. The refill could also be carried out at fleet refueling stations. As more E85 fueling stations become available, the driver will have increased opportunity for refill in a typical manner. An additional refueling option is for the driver or a service station attendant to replenish the octane boost fuel additive tank using containers of E85 or some other form of ethanol.
For a typical light duty truck, the EBS technology is projected to provide a 25% – 30% increase in city-highway efficiency over a state of the art conventional naturally aspirated gasoline engine for a cost of approximately $1,400.
In contrast, a clean diesel provides an equivalent efficiency (in miles/BTU of fuel or the km/gm CO2 standard which is used in Europe) at an incremental cost of around $5,000. The $5,000 cost estimate was given as a representative number by both GM’s Bob Lutz and Frank Klegon, VP Chrysler, at the August 2007 Traverse City Management Briefing Seminar. Thus, EBS technology can provide a very substantial cost savings in addition to the benefit of much greater assurance in meeting future, more stringent air pollutant emission standards, while, at the same time, delivering higher horsepower.
EBS technology can also provide an important cost advantage relative to the full gasoline-electric hybrid, especially for trucks and SUVs that require large, high power engines. The additional cost of the full hybrid powertrain for these vehicles is estimated to exceed $5,000. The EBS technology provides an efficiency gain that is approximately the same as that of present full gasoline-electric hybrids at a much lower cost. The typical city-highway efficiency gain for a full hybrid version of a non-hybrid vehicle is 23% - 33 % according to a recent comparison in the Wall Street Journal using data from Edmunds, a well-respected automotive information research firm (Oct 29, 2007, p. R5). In contrast to EBS technology, hybrids increase powertrain and overall vehicle weight and are, therefore, not as well aligned with the automotive industry’s adjunct goal of reducing vehicle weight for better fuel economy.
Incremental cost divided by percentage efficiency gain has been widely used to compare various options for different technologies. For EBS technology, this parameter has a value of approximately $50 per percent increased efficiency ($50/%) relative to a naturally aspirated gasoline engine. This value is on the order of one-third that of the clean diesel and the full hybrid. Compared to the gasoline turbocharged direct injection engine (GTDI), the EBS engine is projected to increase efficiency by approximately a factor of two and to have an incremental cost/% efficiency parameter which is 40% less than the GTDI engine.
As the E85 infrastructure expands, there will be an increasing market for high efficiency flexible fuel vehicles. EBS technology can be used to enhance the practicality and performance of emerging dedicated E85 fueled vehicle concepts that use direct injection to obtain high performance and high efficiency. These concepts must currently utilize a substantial reduction in turbocharging in order to prevent knock when operated with gasoline alone or with a low concentration ethanol-gasoline blend. Present dedicated E85 fueled vehicle concepts do not provide the desired combination of high efficiency and ability to operate without degraded performance when used as flex fuel vehicles with gasoline operation.
This drawback can be eliminated by use of EBS technology. By employing an additional fuel compartment which is only filled with E85 and where the E85 is used only when needed as an octane boost additive for gasoline operation, the need to reduce performance can be essentially eliminated. It is thus possible to operate with no reduction in torque/power when E85 is not available every time the primary tank is refilled. The E85 in the additional tank could be refilled as infrequently as once every 6 months and, if desired, the extra tank could be topped off every time that the primary tank is filled with E85. The presence of the additional fuel compartment for only E85 effectively guarantees that the vehicle will always have the capability be powered with nearly 100% gasoline without degrading performance. The extra components for obtaining this capability are a second fuel compartment or tank and a set of port fuel injectors. This additional cost is estimated to be around $300.
In addition, the EBS technology avoids the reduced fuel economy (in miles/gallon fuel) that occurs when operating a Flex-Fuel vehicle on E85, because of the decreased energy content of the fuel. Thus, the range of a vehicle with EBS technology would be comparable to that of a naturally aspirated engine operating on gasoline, for same size tank.
EBS technology can also address cold start difficulty and subsequent emission issues that arise when starting on low volatility E85 since starting can be done using gasoline.
EBS technology can also be used with a hybrid powertrain and could be particularly attractive when combined only with a relatively simple engine shutdown-restart capability. The highly downsized EBS engine would be considerably easier to restart than the larger engine that it would replace. This option has not been explored in detail, even by computer modeling. Basic physical considerations indicate that it should add another 5% to10% in efficiency, primarily in congested city driving, bringing the total efficiency gain to well above 30% for combined city/highway driving, with a possible 35% to 40% gain. The cost for the engine shutdown-restart system is preliminarily estimated to be $1,000. Using this estimate, the EBS approach combined with engine shutdown-restart could yield an efficiency gain which is equal to or greater than the present full hybrid at a cost of approximately $2,500 for a light duty truck. The cost per percentage increase in fuel efficiency would be around $70/% efficiency gain. This cost would be about one half or less of that of present full hybrid for light duty trucks.
EBS technology is an attractive replacement for large diesel engines used in heavy duty vehicles that have limited or intermittent operation at very high torque and operate within a confined geographical region. Such vehicles include urban buses, trash haulers/ collectors, cement mixers and a large number of other Class 3 to Class 8 trucks. Because of the limited/intermittent operation at high torque, the knock suppressing second fuel requirement is relatively small. Further, since a large number of these vehicles operate from a central depot, the secondary fuel tank can be refilled as often as necessary. Also, due to centralized refueling, more effective knock suppressing fuels such as highly concentrated methanol could be employed as an alternative to ethanol or E85.
In order to meet current and future emissions regulations, diesel engines in these vehicles employ very high values of exhaust gas recirculation (EGR) in addition to the lean air fuel mixtures generally employed in diesel operation. In order to obtain satisfactory torque output from the engine, high levels of turbocharging are required, with inlet manifold pressures exceeding four times ambient pressure being fairly common. This, in turn, results in very high peak pressures in the cylinders and a resulting increase in engine weight and friction.
The maximum engine speed in these large bore engines is typically limited by the flame diffusion rates of diesel combustion to less than 2000 rpm. EBS technology allows the use of high compression ratio, boosted spark-ignited engines of smaller size operated at the stoichiometric air-fuel ratio and at higher rpm without any EGR requirement for emission control of NOx. Not only it is possible to provide substantially higher torque even with downsized engines, it is also possible to increase rated power by raising the maximum engine speed.
Very importantly, the expensive regenerative particulate filter and various NOx control technologies needed for diesel engine aftertreatment can be eliminated replaced instead by highly efficient 3-way catalysts. Also, the expensive ultra-high pressure fuel injection system for controlling particulates (and noise) can be replaced with a much less costly gasoline type direct injection system. The downsized EBS engine can be many thousands of dollars less expensive than the diesel it replaces without any sacrifice in reliability and durability expected of heavy duty engines (500,000 miles to overhaul).
Methodical engine and knock simulations have indicated that the thermal efficiency of the downsized EBS engine can exceed that of the baseline diesel at medium to high loads while being very slightly less at lighter loads where the overall fuel consumed is lower.
the use of EBS technology, the knock limit on engine performance is essentially
eliminated, thereby allowing operation at a considerably higher compression
ratio (12 or greater) combined with greater turbocharging and downsizing by of
at least a factor of two. These
features along with stoichiometric operation provide highest possible
By controlling the use of E85 to only those times when needed to prevent knock at higher levels of torque, its use can be limited to 5% or less of gasoline use for regular metro/highway driving, including a one-third weighting of the more aggressive US06 cycle. For prolonged towing, the use of the octane boost additive would be greater but could be limited to the 10% range by various measures including appropriate gearing and spark retard as required.
For regular metro/highway driving, refueling could be as infrequent as once every four to six months and could be done at the dealer or at a garage at the same time as regular servicing. Alternatively, the driver or a service station attendant could replenish the octane boost fuel using 1 or 2 gallon containers – similar to the case of using the containers of methanol-water mix that are used as windshield cleaner. 100% methanol containing a small amount of gasoline could, in fact, be used as a backup option to E85. Due to its higher effectiveness in suppressing knock, use of methanol can reduce the octane boost fuel requirement by about a factor of two. The driver could also use one of the limited but rapidly growing number of E85 pumps where available, which now number over 1300 nationwide.
The octane boost fuel additive refill frequency requirements for the EBS technology are similar to those for urea for the SCR aftertreatment for clean diesels. Relative to urea-SCR, the EBS technology has the advantage that ethanol distribution centers near service stations (for blending with gasoline) already exist and E85 is already available at over 1300 service stations. Moreover, if ethanol or methanol is not available, the vehicle can still be operated at approximately 50% of full power through the use of premium fuel in both tanks.
Engine dynamometer tests have proven the virtual elimination of the knock constraint for gasoline (spark-ignited) engine operation and indicate major potential benefits from the use of EBS technology. Gasoline engines that use EBS technology can provide diesel-equivalent efficiency and equal or higher torque at much lower cost, while also providing low emission levels that will insure meeting potentially more stringent emission standards in the future. The use of EBS technology in gasoline engines can also provide approximately the same efficiency gain as either clean diesel or typical gasoline-electric hybrids in realistic city/highway driving. In addition, EBS technology can also provide a higher horsepower than the clean diesel or the hybrid and more useable interior space than the hybrid vehicle.
The technology is also well aligned with the growing interest and availability of E85 and enhances the attractiveness of flex fuel vehicles. EBS technology can be particularly important in providing a means to obtain high efficiency in cars and light duty trucks in a manner that is affordable, clean and can be implemented in the near term.