Hybrid powertrains that use compressed air to help power a vehicle could dramatically improve the fuel economy, particularly in cities and urban areas where the traffic conditions involve a lot of starts and stops. In such conditions, a large amount of fuel is needed to accelerate the vehicle, and much of this is converted to heat in brake friction during decelerations. Capturing, storing and reusing this braking energy to produce additional power can therefore improve fuel efficiency. In this study, three approaches towards air hybrid powertrains are proposed and analyzed. In the first approach, an energy recovery valve or two shut-off valves connected to a convenient access hole on the engine cylinder is proposed to enable the cylinder to operate as a regenerative compressor and/or expander when required. In the second approach, one of the exhaust valves in an engine equipped with a Fully Variable Valve Actuation (FVVA) system is pneumatically or hydraulically operated as a dedicated gas transfer valve connected to an air reservoir. The third approach combines the advantages of the conventional valvetrain’s simplicity with emerging production technologies. In order to achieve this, two well established technologies are used in addition to valve deactivation; Variable Valve Timing (VVT) and/or Cam Profile Switching (CPS). Provided that a conventional, camshaft-operated variable valvetrain is used, the need of adopting fully variable valve actuation is eliminated and thus only minor modifications to the engine architecture are required. The aforementioned concepts are described in details. Some basic principles of their operation are also discussed in order to provide a better understanding on how fuel economy is achieved by means of engine hybridization and regenerative braking. Both experimental and computational results are presented and compared. Finally, a vehicle and driveline model, which simulates the operation of a typical passenger vehicle in urban driving conditions and predicts the efficiency of the energy regeneration, has been set up and used to study the effects of the application of each air hybrid concept on the vehicle’s energy usage throughout the New European Driving Cycle (NEDC) and the 10-15 driving cycle. The results have shown that each concept involves the optimization of valve timing for the best regenerative energy recovery and its subsequent usage. For the modelled vehicle, it has been shown that any of the three concept engines is capable of providing more braking power than needed during every deceleration and braking process, especially throughout the urban driving part of each cycle. The recovered braking energy in the form of compressed air has proved to be always sufficient to start the engine, if stop-and-start engine operation strategy is to be adopted.

<div>Strict emissions regulations are mandated by the environmental protection agency (EPA) to reduce emission of greenhouse gases and criteria air pollutants from diesel engines, which are widely used in commercial vehicles. A ten-fold reduction in allowable heavy-duty on-road oxides of nitrogen (NOx) emissions are projected to be enforced by 2024. The need to meet these emission regulations, along with consumer demand for better fuel efficiency, has resulted in greater effort towards cleaner and more efficient diesel engines.</div><div><br></div><div><div>Diesel engine aftertreatment systems are effective in reducing engine-out emissions, but only at catalyst bed temperatures above 200°C. The aftertreatment system needs to be quickly warmed up to its efficient operating temperatures, and maintain elevated temperatures in a fuel-efficient manner, which is a challenge using conventional engine strategies. This study details the use of advanced gas-exchange management, via variable valve actuation, to improve both `warm-up' and `stay-warm' aftertreatment thermal management.</div></div><div><br></div><div><div>Fast initial warm-up of the aftertreatment system, following a cold engine start, is enabled by strategies such as early exhaust valve opening (EEVO), internal exhaust gas recirculation (iEGR) and late intake valve closure (LIVC). Steady state and drive cycle results of a combination of EEVO and iEGR at idle operation, and a combination of EEVO and LIVC at off-idle conditions below 7.6 bar BMEP, are presented. It is demonstrated that ~ 150°C higher steady state temperatures are achieved at idle, and up to 10.1% reduction in predicted tailpipe-out NOx is achieved at 3.1% fuel penalty over the heavy-duty federal test procedure (HD-FTP) drive cycle.</div></div><div><br></div><div><div>Fuel-efficient `stay-warm' aftertreatment thermal management is demonstrated to be effectively achieved via cylinder deactivation (CDA), to reduce fuel consumption, elevate engine-outlet temperatures and reduce exhaust flow rates at idle and low load engine operation. Implementation of CDA at idle and low loads below 3 bar BMEP is demonstrated to achieve fuel savings of 4% over the HD-FTP drive cycle, while maintaining similar levels of tailpipe-out NOx emissions. It is demonstrated that lower air flow during CDA at, and near, idle operation does not compromise the transient torque/power capabilities of the engine- a key nding in enabling the practical implementation of CDA in diesel engines.</div></div><div><br></div><div><div>Some of the practical challenges expected with CDA are studied in detail, and alternate strategies addressing the challenges are introduced. Dynamic cylinder activation (DCA) is introduced as a means to enable greater control over the torsional vibration characteristics of the engine, via selection of appropriate ring patterns, while maintaining similar performance and emissions as xed CDA. A generic strategy to use CDA and an appropriate DCA strategy to operate away from driveline resonant frequencies at different engine speeds is described. Ventilated cylinder cutout (VCC) is introduced as a means to potentially mitigate oil accumulation concerns during CDA, by ventilating the non-ring cylinders to the intake/exhaust manifold(s) by opening the intake/exhaust valves during all the four strokes of the engine cycle. The fuel efficiency and thermal management performance of VCC is assessed for different ventilation congurations and compared with CDA and baseline engine operation.</div></div>

The automotive industry has been in a marathon of advancement over the past decades. This is partly due to global environmental concerns about increasing amount of air pollutants such as NOx (oxides of nitrogen), CO (carbon monoxide) and particulate matters (PM) and decreasing fossil fuel resources. Recently due to stringent emission regulations such as US EPA (Environmental Protection Agency) and CARB (California Air Resource Board), improvement in fuel economy and reduction in the exhaust gas emissions have become the two major challenges for engine manufacturers. To fulfill the requirements of these regulations, the IC engines including gasoline and diesel engines have experienced significant modifications during the past decades. Incorporating the fully flexible valvetrains in production IC engines is one of the several ways to improve the performance of these engines. The ultimate goal of this PhD thesis is to conduct feasibility study on development of a reliable fully flexible hydraulic valvetrain for automotive engines. Camless valvetrains such as electro-hydraulic, electro-mechanical and electro-pneumatic valve actuators have been developed and extensively studied by several engine component manufacturers and researchers. Unlike conventional camshaft driven systems and cam-based variable valve timing (VVT) techniques, these systems offer valve timings and lift control that are fully independent of crankshaft position and engine speed. These systems are key technical enablers for HCCI, 2/4 stroke-switching gasoline and air hybrid technologies, each of which is a high fuel efficiency technology. Although the flexibility of the camless valvetrains is limitless, they are generally more complex and expensive than cam-based systems and require more study on areas of reliability, fail safety, durability, repeatability and robustness. On the contrary, the cam-based variable valve timing systems are more reliable, durable, repeatable and robust but much less flexible and much more complex in design. In this research work, a new hydraulic variable valve actuation system (VVA) is proposed, designed, prototyped and tested. The proposed system consists of a two rotary spool valves each of which actuated either by a combination of engine crankshaft and a phase shifter or by a variable speed servo-motor. The proposed actuation system offers the same level of flexibility as camless valvetrains while its reliability, repeatability and robustness are comparable with cam driven systems. In this system, the engine valve opening and closing events can be advanced or retarded without any constraint as well as the final valve lift. Transition from regenerative braking or air motor mode to conventional mode in air hybrid engines can be easily realized using the proposed valvetrain. The proposed VVA system, as a stand-alone unit, is modeled, designed, prototyped and successfully tested. The mathematical model of the system is verified by the experimental data and used as a numerical test bench for evaluating the performance of the designed control systems. The system test setup is equipped with valve timing and lift controllers and it is tested to measure repeatability, flexibility and control precision of the valve actuation system. For fast and accurate engine valve lift control, a simplified dynamic model of the system (average model) is derived based on the energy and mass conservation principles. A discrete time sliding mode controller is designed based on the system average model and it is implemented and tested on the experimental setup. To improve the energy efficiency and robustness of the proposed valve actuator, the system design parameters are subjected to an optimization using the genetic algorithm method. Finally, an energy recovery system is proposed, designed and tested to reduce the hydraulic valvetrain power consumption. The presented study is only a small portion of the growing research in this area, and it is hoped that the results obtained here will lead to the realization of a more reliable, repeatable, and flexible engine valve system.

The automotive industry has been in a marathon of advancement over the past decades. This is partly due to global environmental concerns about increasing amount of air pollutants such as NOx (oxides of nitrogen), CO (carbon monoxide) and particulate matters (PM) and decreasing fossil fuel resources. Recently due to stringent emission regulations such as US EPA (Environmental Protection Agency) and CARB (California Air Resource Board), improvement in fuel economy and reduction in the exhaust gas emissions have become the two major challenges for engine manufacturers. To fulfill the requirements of these regulations, the IC engines including gasoline and diesel engines have experienced significant modifications during the past decades. Incorporating the fully flexible valvetrains in production IC engines is one of the several ways to improve the performance of these engines. The ultimate goal of this PhD thesis is to conduct feasibility study on development of a reliable fully flexible hydraulic valvetrain for automotive engines. Camless valvetrains such as electro-hydraulic, electro-mechanical and electro-pneumatic valve actuators have been developed and extensively studied by several engine component manufacturers and researchers. Unlike conventional camshaft driven systems and cam-based variable valve timing (VVT) techniques, these systems offer valve timings and lift control that are fully independent of crankshaft position and engine speed. These systems are key technical enablers for HCCI, 2/4 stroke-switching gasoline and air hybrid technologies, each of which is a high fuel efficiency technology. Although the flexibility of the camless valvetrains is limitless, they are generally more complex and expensive than cam-based systems and require more study on areas of reliability, fail safety, durability, repeatability and robustness. On the contrary, the cam-based variable valve timing systems are more reliable, durable, repeatable and robust but much less flexible and much more complex in design. In this research work, a new hydraulic variable valve actuation system (VVA) is proposed, designed, prototyped and tested. The proposed system consists of a two rotary spool valves each of which actuated either by a combination of engine crankshaft and a phase shifter or by a variable speed servo-motor. The proposed actuation system offers the same level of flexibility as camless valvetrains while its reliability, repeatability and robustness are comparable with cam driven systems. In this system, the engine valve opening and closing events can be advanced or retarded without any constraint as well as the final valve lift. Transition from regenerative braking or air motor mode to conventional mode in air hybrid engines can be easily realized using the proposed valvetrain. The proposed VVA system, as a stand-alone unit, is modeled, designed, prototyped and successfully tested. The mathematical model of the system is verified by the experimental data and used as a numerical test bench for evaluating the performance of the designed control systems. The system test setup is equipped with valve timing and lift controllers and it is tested to measure repeatability, flexibility and control precision of the valve actuation system. For fast and accurate engine valve lift control, a simplified dynamic model of the system (average model) is derived based on the energy and mass conservation principles. A discrete time sliding mode controller is designed based on the system average model and it is implemented and tested on the experimental setup. To improve the energy efficiency and robustness of the proposed valve actuator, the system design parameters are subjected to an optimization using the genetic algorithm method. Finally, an energy recovery system is proposed, designed and tested to reduce the hydraulic valvetrain power consumption. The presented study is only a small portion of the growing research in this area, and it is hoped that the results obtained here will lead to the realization of a more reliable, repeatable, and flexible engine valve system.

The restrictions imposed by CO2 emission standards in Europe and many countries have promoted the development of more efficient spark ignition engines. The reduced swept volume and number of cylinders of four-stroke engines has significantly improved fuel economy by means of lower pumping and friction losses. This approach, known as engine downsizing, has demonstrated its potential of reducing fuel consumption on its own as well as applied to hybrid vehicles where a low weight engine is desired. However, aggressive engine downsizing is currently constrained by thermal and mechanical stresses and knocking combustion. In order to overcome these limitations, the present work evaluates the application of a conventional poppet valve direct injection engine into the two-stroke cycle. Two-stroke engines have the ability to produce higher power with reduced swept volume and less weight than four-stroke engines thanks to the doubled firing frequency. These advantages, although, are sometimes offset by poorer emissions resulted from fuel short-circuiting; lower thermal efficiency resulted from short expansion process; and reduced engine durability due to lubrication issues. Therefore, in this research the four-stroke engine architecture was employed so these shortcomings could be addressed by the use of direct fuel injection, variable valve actuation and a wet crankcase, respectively. The burnt gases were scavenged during a long valve overlap by means of boosted air supplied by an external compressor. An electrohydraulic fully-variable valve train enabled the optimisation of the gas exchange process in a variety of engine operating conditions. The air-fuel mixture formation was evaluated through computational fluid dynamic simulations and correlated to experimental tests. In addition, the engine operation with ethanol was assessed in a wide range of engine loads and speeds. Finally, the engine performance, combustion process, air-fuel mixing and gas exchange results were presented, discussed and contextualised with current four-stroke engines. Keywords: Two-stroke poppet valve engine; gasoline and ethanol direct injection; engine downsizing; supercharged two-stroke cycle.

<p>  </p> <p>A Cummins 6.7L natural gas engine enabled with VVA was installed in a research test cell at Purdue’s Ray Herrick Laboratories for experimental testing. The stock engine which was connected to an AC dynameter was mounted on a movable test bed outfitted with numerous sensors, a charge air cooler, and an external heat exchanger. In the engine control room, a few different systems were set up to run the dyno, collect data from the engine sensors, and monitor the safety apparatuses in the test cell. </p> <p>After the test cell setup was completed, an initial baseline testing was performed to compare the stock engine operation with the baseline engine data given in the Cummins fuel map. The testing was used to verify the engines stock functionality and troubleshoot some additional issues before setting the boundary conditions. Once the boundary conditions were set, a final stock engine testing was performed at rated to check for repeatability and verify stock engine operation following the engine modifications made to accommodate the VVA. </p> <p>Following the baseline testing, the VVA system was assembled on the standalone rig to verify its operation before mounting it on the engine. In order to run the natural gas valve profiles received from Cummins, the VVA controller gains were retuned and the LVDT sensors were calibrated so that the desired closing, opening and lift behaviors were achieved. After verifying the VVA’s functionality, the hardware was mounted on the engine for the VVA experimental testing. </p> <p>The initial VVA testing was focused on understanding the impacts of intake valve modulation on the gas exchange process. Based on previous simulation work, reductions in pumping work leading to better fuel economy is one expected outcome. Experimental testing data related to the engine performance and operation was used to compare each IVC case to the stock IVC timing. These results were also compared to the previous GT-Power work to identify any apparent trends.</p> <p>Future work includes using VVA to further improve efficiency in the part load region, and reduce knock at higher loads. Additionally, the incorporation of a laser based in-cylinder sensing system will help to optimize the capability of VVA.</p>

The transportation sector continues to be a primary source of greenhouse gas (GHG) emissions, contributing more than any other sector in the United States in 2017. Medium-duty and heavy-duty trucks trail only passenger cars as the largest GHG contributor in this sector [1]. The intense operating requirements of these vehicles create a reliance on the diesel engine that is projected to last for many decades. Therefore, it is vital that the efficiency and environmental sustainability of diesel engines continue to be advanced.<br><br>Cylinder deactivation (CDA) is a promising technology to improve diesel engine fuel efficiency and aftertreatment thermal management for emissions reduction. This work presents original experimental results demonstrating fuel efficiency improvements of CDA implemented on a modern engine at idle operating conditions through testing of various CDA configurations. Idle calibration optimizations result in up to 28% fuel consumption reduction at steady-state unloaded idle operation and 0.7% fuel consumption reduction over HD-FTP drive cycles at equivalent emissions levels. The low-load thermal management performance of CDA is also investigated through creep and extended idle transient cycles, during which CDA is shown to reduce fuel consumption by up to 40% with similar thermal management performance and reduced NOx and soot emissions. <br><br>Variants of CDA implementation are explored through an experimental comparison of deactivation strategies. The effort described here compares charge trapping strategies through examination of in-cylinder pressures following deactivation because: (1) choice of trapping strategy dictates the in-cylinder pressure characteristics of the deactivated cylinders, and (2) deactivated cylinders can affect torque, oil consumption, and emissions upon reactivation. Results discussed here suggest no significant differences between the strategies. As an example, the in-cylinder pressures of both trapping strategies are shown to converge as quickly as 0.8 seconds after deactivation.<br><br>Finally, the NVH effects of CDA are characterized through studies of torsional vibration, linear vibration, and acoustics. CDA causes frequency content at reduced frequencies compared to conventional operation, which has effects on all aspects of NVH. This creates possible constraints on achievable fuel efficiency and thermal management performance by restricting CDA usage. An alternate form of CDA, dynamic cylinder activation (DCA), is explored as a possible option of avoiding undesirable frequency output while maintaining the desired engine performance. <br>

A new camless electrohydraulic valve train concept for combustion engines was developed at Empa (Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland) and tested on a spark ignition passenger car engine. Besides full flexibility with regard to lift and timing of the engine gas exchange valves it features robustness, simplicity and in particular a low own drive power need due to a maximum of hydraulic energy recuperation. The engine test results confirm substantial efficiency gains in classical as well as in hybrid power trains while also maintaining additional advantages. The system also has the potential to become a key element for load control of piston based compressors and expanders, reciprocating Joule Cycle engines and derivable future electricity storage systems.