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The air-hybrid engine absorbs the vehicle kinetic energy during braking, puts it into storage in the form of compressed air, and reuses it to assist in subsequent vehicle acceleration. In contrast to electric hybrid, the air hybrid does not require a second propulsion system. This approach provides a significant improvement in fuel economy without the electric hybrid complexity. The paper explores the fuel economy potential of an air hybrid engine by presenting the modeling results of a 2.5L V6 spark-ignition engine equipped with an electrohydraulic camless valvetrain and used in a 1531 kg passenger car. It describes the engine modifications, thermodynamics of various operating modes and vehicle driving cycle simulation. The air hybrid modeling projected a 64% and 12% of fuel economy improvement over the baseline vehicle in city and highway driving respectively.

Using an electric hybrid leads to a significant improvement in vehicle fuel economy. Unfortunately, it also leads to a substantial increase in cost. Regenerative compression braking offers another way to achieving the same objective without incurring the same cost penalty. With some modifications, the vehicle engine can perform both absorption and recovery of braking energy, using compressed air for energy storage. The process parallels the one employed by electric hybrids, but it requires none of the expensive electric equipment used in hybrid systems. This paper reviews basic principles of regenerative compression braking and its advantages in comparison to electric hybrid systems. It also describes the required changes in engine system and methods of control. Description and mathematical analysis of applicable thermodynamic cycles is given, including computations of cycle efficiencies and indicated mean effective pressures produced during braking and acceleration.

A typical pattern of vehicle driving includes a series of frequent accelerations and decelerations. Fuel energy spent to accelerate the vehicle is later wasted during deceleration, when kinetic energy is converted into heat in friction brakes. New thermodynamic cycles have been conceived for automobile engines to capture the energy of braking in the form of compressed air, and reuse this energy during acceleration at a later time. They are applicable to all types of automotive engines. Each four-stroke cycle includes two power strokes, one with compressed air and a second one with combustion gas. It is also possible to switch the engine operation from a four-stroke to a two-stroke cycle during acceleration, which allows a reduction in engine displacement.

An experimental engine with an electrohydraulic camless valvetrain, capable of total valve motion control, was built at Ford Research Laboratory. The system uses neither cams, nor springs, which reduces the engine height and weight. Hydraulic force both opens and closes the valves. During the valve acceleration, potential energy of compressed fluid is converted into kinetic energy of the valve. During deceleration, the energy of the valve motion is returned to the fluid. Recuperation of kinetic energy is the key to the low energy consumption. The system offers a continuously variable and independent control of virtually all parameters of valve motion. This permits optimization of valve events for each operating condition without any compromise.

The effect of port injected small fuel droplets was evaluated for several different modes of engine operation. The droplets were generated by an Air Forced Injector (AFI), Figure 1, which uses high velocity air through a nozzle to produce fuel droplets on the order of 10mm Sauter Mean Diameter (SMD). AFI results were compared to those from a standard production pintle injector. Steady state data, “motored cold start” data, and injector cut-out data were collected. All three data sets illustrate functional advantages of AFI over standard Electronic Fuel Injection (EFI). Steady state testing showed that the AFI delivers complete freedom for specifying injection timing with respect to HC emissions. This freedom is highly advantageous for transient conditions because open valve injection with small droplets causes much less port wall wetting. Therefore, less control system compensation is necessary, and more accurate air-fuel ratio control is achievable.

Two-stroke gasoline engines are known to benefit from using in-cylinder fuel injection which improves their ability to meet the strict fuel economy and exhaust emissions requirements. A conventional method of in-cylinder fuel injection involves application of plunger-type positive displacement pumps. Two-stroke engines are usually smaller and lighter than their 4-stroke counterparts of equal power and need a pump that should also be small and light and, preferably, simple in construction. Because a 2-stroke engine fires every crankshaft revolution, its fuel injection pump must run at crankshaft speed (twice the speed of a 4-stroke engine pump). An electronically controlled fuel injection system has been designed to satisfy the needs of a small automotive 2-stroke engine capable of running at speeds of up to 6000 rpm.

Late fuel injection directly into the cylinder of a 2-stroke engine is desirable to prevent escape of some fuel into exhaust system during cylinder scavenging. This leaves little time for fuel evaporation and mixture preparation and puts a premium on the degree of fuel atomization needed during the injection process. Although a respectable degree of atomization can be attained in fuel systems with high pressure, liquid-only injection, further improvements can be made when compressed air is used to assist atomization. A novel air-forced (AFI) fuel injection system for in-cylinder injection in a 2-stroke engine is described. The system employs compressed air to force a metered quantity of fuel from the fuel injector internal cavity past a spring loaded poppet valve. A fog-like cloud containing a rich mixture of fuel and air is injected into the cylinder. As a result, an exceptionally fine atomization is achieved.

With the advent of electronic controls and development of electromagnetically controlled fuel injection pumps, the cost of fuel systems using plunger-type pumps was substantially reduced. Further reduction in cost can be achieved if fewer solenoid valves are used. A new type of injection pump combining electromagnetic spill control principle with distributor-type operation is described. Only one solenoid valve is required for a multi-cylinder engine. The pump was designed for port injection of gasoline, but with some modifications could be adapted to direct fuel injection. The fuel injection system includes a controller capable of electronic trimming of port-to-port fuel distribution for tight control of air to fuel ratios in all engine cylinders. A review of the basic concept and operating principles is given, and test results as well as cost considerations are discussed.

Usage of solenoid valves capable of controlling fuel delivery to several engine cylinders in succession reduces the cost and complexity of electromagnetic fuel injection systems. A new type of injection pump employing solenoid valves with shuttles is described. In a multiplunger pump such a solenoid valve controls operation of two plungers in succession. The number of required solenoids is equal to half the number of engine cylinders. A review and analysis of the basic concept is given, and test results are discussed.

The high cost and complexity of fuel injection pumps are major factors limiting the application of direct fuel injection in internal combustion engines. Recent advances in electronics offer an opportunity for an improvement in this situation. A review and analysis of the electromagnetic spill control concept, in which the pump governor is replaced by solenoid valves, is given. An experimental electromagnetic fuel injection pump and its electronic control system are described, and test results are discussed.

The growing need for solenoid actuators capable to provide both high traction force and fast response is reviewed. A new concept of a fast response multipole solenoid is described, and a discussion of factors leading to faster solenoid response is given, An improved schedule of energy input into the solenoid coil is suggested, and an analysis of the dynamics of the armature motion and its correlation with changing electric and magnetic parameters during the solenoid activation period is performed.