“If you look at the basics of an engine, it is a pretty simple machine to start with,” said Dr. Charles Roberts, Manager of Advanced Combustion and Emissions for Southwest Research Institute (SwRI), speaking at the SAE International 2012 High Efficiency IC Engines Symposium on April 23. “It is a big air pump that you put some fuel into—burn that fuel to get useful work.” He said the proven way to increase the efficiency of an engine using the standard Otto cycle, typical in practically all vehicles today, is to select the right working fluid and increase the compression ratio until side effects such as heat loss or friction dominate any gains. While compression ignition (CI) engines (diesel) have compression ratios higher than spark ignition (SI) (gasoline), and therefore higher efficiencies, there remains opportunities to improve both. “Even though production SI engines now run about 32% efficiency, there are 40% efficient SI engines in research and development right now,” he stated.
He notes a number of technologies that improve gasoline engines that will cost somewhere between $25-50 per 1% of fuel-economy improvement. Diesel technologies to improve fuel economy will be a bit more expensive, between $50-100 per 1% of fuel-economy improvement. This is primarily because diesel is already so efficient compared to SI.
SwRI is leading two consortium for improving the basics of engine technology. One is The High-Efficiency Dilute Gasoline Engine (HEDGE), aimed at meeting the performance, durability, and emissions requirements of future motor vehicles. The other is the Clean High-Efficiency Diesel Engine VI Consortium. Started in November 2011, it will develop diesel engine technology to meet the needs of industry five to 10 years into the future.
EcoBoost today and in the future
Dr. Eric Curtis was on hand to discuss Ford’s strategy to meet near-term goals for gasoline fuel efficiency. Its main strategy is in improving the company’s EcoBoost GTDI (gasoline turbocharged direct injection) technology. “Gasoline direct injection charge cooling enables a higher CR,” said Curtis, improving efficiency. The higher charge density of direct injection increases performance over port-fuel injected (PFI) engines,” explained Curtis. He went on to note that a ‘high-efficiency engine’ is efficient when it best matches the loads required of it, such when used in Federal Test Procedure (FTP) drive cycles. He presented data that showed the benefit of a downsized GTDI engine is significant when used on these FTP drive cycles.
“90% of Ford nameplates will have EcoBoost by 2013,” he stated.
He also discussed how Ford is looking to further improve EcoBoost, as well. He presented data that showed that both downsizing and reducing the running speed both minimize pumping and friction losses. He also presented simulated data that showed reducing the number of cylinders reduces thermal losses, such as eight cylinders to six, or six cylinders to four, within limits of NVH issues. Another challenge he described was knock limits at high loads. Cooled exhaust gas recirculation (EGR), late intake valve closing (LIVC), scavenging, and other engine technologies could provide even higher compression ratios (CRs).
What’s next for Ford? Curtis described in some detail longer term technology opportunities that include advanced lean combustion with direct fuel injection and advanced ignition. Such technologies could include lean combustion modes such as homogenous, stratified, homogenous charge compression ignition (HCCI), or an ‘optimum stratified’ mode that is stable and produces low PM and low NOx.
BorgWarner reduces pumping losses
Reducing pumping losses was the focus of a presentation from BorgWarner, given by Christopher Thomas, Vice President of Advanced Engineering, Engine Group. His presentation showed two methods for reducing pumping losses in four-stroke SI engines. One he described as Valve Event Modulated Boost (VEMB), directed at turbocharging. As Thomas described it, VEMB allows separation of two parts of an exhaust event, the early, or blow-down stage, and a later, or scavenge stage. The VEMB allows the turbo to capture the blow down energy and avoids pumping work through the turbocharger. (SAE paper 2012-01-0705, available here, describes the VEMB results in depth.) Tests the company conducted observed from 2 to 12% improvement in fuel consumption using VEMB. With potential to increase CR and re-burning hydrocarbons from the scavenge stream with EGR, Thomas believes the total possible benefit is 6-17% over already-downsized turbocharged engines.
The second was a ‘virtual cylinder deactivation’ using BorgWarner’s high speed Cam Torque Actuated (CTA) Phaser. “We get 90% of the benefits of cylinder deactivation with virtually zero cost,” explained Thomas. “We phase the intake and the exhaust about 95 degrees.” In his presentation, he described the virtual cylinder deactivation as working naturally on a V6 because of the firing order, with a bank of three cylinders deactivated at any given time, by simply moving the phases. Key enablers he described include: phasing the camshafts need to occur within one or two cam events, CTA to phase fast enough, extended range of authority, and a Mid Position Lock device that is required to start the engine with extended range of authority. While delivering 4.5% to 8% better fuel economy, he describes the technique as having no effect on valvetrain dynamics, valvetrain packaging, or port packaging and may not require special NVH countermeasures. “Total cost of implementation is less than $10 per 1% of fuel-economy improvement,” he stated.
Honeywell puts pumping to work
Mike Guidry, Manager of Advanced Technologies for Honeywell Transportation Systems, presented his company’s novel approach to reducing pumping losses, its ThrottleCHARGER device. This is an integrated turbine/generator device that generates electricity by recovering pumping work. “Experiments in this idea have been performed going back 30 years,” said Guidry in a presentation during the session.
Why is it important now? He points to the continuing pressure to increase fuel economy and the fact that vehicles today and into the future have dramatically increased electric loads. ”What we did is stick a turbine generator on a throttle,” explained Guidry. “It still operates like a throttle, but the generator increases fuel economy by reducing alternator load.”
The charger increases fuel-economy benefits by up to 5%. Guidry describes the device as more useful when there is more electrification, such as in mild hybrids and/or with idle-stop devices. A conventional MY 2010 light truck with a V8 might only use on average 150+ watts. Electrify that vehicle and equip it with an idle-stop and it might draw up to 450 watts average electric load. According to Honeywell’s data, the fuel-economy benefit at 154 watts is about 1.3%; at 450 watts it rises to 3.2%. All in a cost-effective design that requires simple controls, according to Guidry. The maximum benefit of the device might be as high as 4%.