THE ECOBOOST ENGINE: COMBINING VARIABLE VALVE TIMING ...

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Neil Debski Seth Kahanov FIGURE 3 Visual of a Camshaft [16] The phase adjustment results in a change to the pump work required by the engine to accomplish the gas exchange process [12]. The majority of current cam phaser applications use hydraulically-actuated units, powered by engine oil pressure and managed by a solenoid that controls the oil pressure supplied to the phaser [15]. Concentric camshafts allow for two independent variable valve timing on a single camshaft. Intake and exhaust centerline timings are controlled to give prime engine performance over the all operating ranges. A benefit from the twin independent variable camshaft timing is a reduction in emissions when the throttle, that controls the flow of fuel to the engine is partially open [15]. Lower emission, combined with control of nitrous oxides and hydrocarbons at all engine speeds, reduces atmospheric pollution. From a physics standpoint, variable valve timing can also be used to reduce the work required by the piston to pump the combustion gasses into and out of the combustion chamber. At any specific speed and load, increasing the intake of air into the combustion chamber allows the engine to burn more fuel, thus resulting in more power being produced. Concentric camshafts allow for a 5% increase in fuel economy as well as a 10% increase of mean torque [15]. This is measured in terms of an engine’s volumetric efficiency (the actual volume induced divided by the static cylinder volume). Variable camshaft timing is electronically controlled by hydraulic valves that direct high pressure engine oil into the camshaft phaser cavity. Gasoline direct injection engines are combined with variable valve timing to create a large improvement in part load economy due to the reduction in pumping losses. This improvement stems from the homogeneous mixture of air and fuel at all engine speeds and loads causing a stratified charge. Stratified processes allow for a smaller dependence on a throttle in the intake system as small quantities of fuel can be added to excess air [15]. The final component that increases the EcoBoost’s benefits will be described in the next section with turbocharging. <strong>THE</strong> <strong>ECOBOOST</strong>’S EFFICIENT TURBO- CHARGING The final aspect that makes the EcoBoost engine efficient is its turbocharger. A turbocharger is a compressor that forces a greater quantity of the fuel and air mixture into the engine’s intake and pistons. The compressor wheel is spun by an attached turbine wheel, which utilizes exhaust coming from the engine. The spinning wheel of the turbine has fan blades that compress the air that forces its way to the cylinder intake, as seen in Figure 4. Due to the increased mass of airborne gasoline in the cylinder, the combustion forces the piston down at a higher speed increasing torque. A turbocharger can decrease the engine’s specific fuel consumption by as much as 14% [17]. FIGURE 4 Processes of a Turbo-charge [17] The EcoBoost engine uses two Honeywell GT15 turbochargers with water-cooled bearings. These watercooled and oil-cooled turbos are quite unlike the turbos from the 1980s that were cooled only by engine oil. The EcoBoost turbo bearings are water-cooled in the same coolant loop as the engine to bring turbo temperatures down. A general rule for turbocharging is to use the smallest turbocharger possible that provides the desired performance. This is done to minimize turbo lag. Turbo lag is caused by the short time lapse between the moment the accelerator is depressed and the turbocharger response from the exhaust fumes. As stated, a turbocharger must have exhaust fumes to fill the turbine housing in order for the turbocharger to spin and perform its job. This problem is minimized with a small turbocharger because it takes less exhaust pressure to spin a smaller turbine. However, at faster speeds, a larger turbocharger is capable of providing a greater power boost to the engine [17]. Since turbochargers give engines lower specific fuel consumption, the engines output more overall power for less fuel burned. Manufacturers like Ford are looking at benefits that are not simply related to improving a car's speed. A turbocharger on a smaller engine can output the same power as a larger engine for less fuel. Furthermore, because the car will weigh less with a smaller engine, the smaller turbocharged engine will have better performance than the original large engine without a turbocharger [17]. Direct injection uses a much higher pressure system (up to 3000 PSI vs. 100 PSI for normal fuel injection) and sprays the fuel into each cylinder during the compression stroke [13]. Direct injection allows for a better fuel-air mixture inside the cylinder, but it has some other benefits as well, especially with turbocharged engines. For instance, if the air and fuel 4
Neil Debski Seth Kahanov mixture gets too hot, it can prematurely detonate “knock” in the cylinder during the compression stroke and before the spark plugs fire. Preventing this knocking is why additives like lead (and more recently MTBE) are added to gas [13]. Forcing additional air into an engine’s combustion chambers with a turbocharger definitely boosts power. As stated, in order to avoid harmful detonation, turbocharged engines needed lower compression ratios, which compromised efficiency. Direct fuel injection helps solve this problem by cooling the intake charge to minimize detonation. Second, if the variable valve timing extends the time when both the intake and the exhaust valves are open, the turbocharger can blow fresh air through the cylinder to completely remove the hot leftover gases from the previous combustion cycle. Since the injectors squirt fuel only after the valves close, none of it escapes through the exhaust valve, improving efficiency and temperature. This turbocharger maximizes the engine’s performance when it is working seamlessly with the engine’s direct fuel injection and variable valve timing. The EcoBoost engine uses two turbos, one per bank. These fixed vane turbos operate in parallel, meaning they operate independently of one another. Smaller turbos enable faster spool-up, allowing for faster peak torque, and reduction in turbo lag. By being mounted close to the cylinder heads, the NVH (noise, vibration, harshness) of the turbo operation is improved compared to older systems, and reduce under hood heat. These smaller turbos spin up faster, kick in at lower engine rpms, operate at higher turbine rpms, and are fully connected to modern powertrain controllers [14]. A turbocharger utilizes forced induction in order to allow more power to be produced for an engine. The turbine wheel is coupled to a compressor that pressurizes air coming into the engine — this is called “boost” and allows the engine to breathe in air as if it were larger in displacement since more air is “forced” into the intake [14]. Fortunately, internal combustion engines have an abundant source of energy that normally goes to waste right out the exhaust pipe. Turbochargers harness the thermal and kinetic energy in the exhaust gases to drive turbines and compressors that force more air into the engine for a big increase in power [14]. The more air an engine intakes, the more power it generates. Engine coolant is responsible for about 60 percent of the engine cooling, while engine oil handles about 40 percent of the cooling [14]. Ford has a unique twist on this. The EcoBoost engine delivers a short spray of oil to the underside of each piston. Squirt jets deliver a 25 psi dose of oil on each piston stroke. This does two things. On a cold start, this helps to quickly warm the oil to operating temperatures, which lowers internal friction and improves fuel economy. Under normal operating conditions, of course, the oil squirt keeps the piston temperatures under cooler levels. ECONOMIC ETHICS The EcoBoost’s decrease in fuel waste has led to a more beneficial fuel economy compared to other engine technologies. The initial problem when facing the fuel economy of conventional engines was balancing the necessary decrease in fuel consumption, while still using enough fuel to increase the performance of the engine. Most automotive companies have initially been reluctant to decrease their fuel consumption because it would “compromise the present performance, reliability, and speed flexibility” [5]. This problem only lead to a compromise before the focus of new designs was direct fuel injection. With this new decrease in fuel waste, Ford did not have to compromise their engine’s performance since their engine utilized the majority of its fuel to increase its efficiency. This is why Ford has improved their fuel economy, because they provided better performance with less fuel consumption than the conventional diesel engine. In comparison to standard diesel engines, the EcoBoost “achieves 365 horsepower at 5,000 rpm and 420 foot-pounds of torque at just 2,500 rpm” [3]. This allows the EcoBoost to continue to perform with high quality at high speeds while diesel engines “run out of steam at higher engine speeds” [3]. This improvement in technology has solved a very large problem that is faced by drivers on a day to day basis. As peoples’ need for efficient transportation increases, they do not have the time or money to waste during constant trips to the gas station. However, this is what happened in the past with regular diesel technology, when higher speeds led to a bigger waste of fuel and less efficient performance. However, with the EcoBoost’s compact design that minimizes fuel waste, less money is spent on gas since the fuel is being utilized in the engine instead of released into the environment. With the EcoBoost’s direct injection technology, the engine is able to use all of the fuel that is applied to it to have the entire engine function for a longer period of time, which results in a better fuel economy. This efficient fuel economy is due the EcoBoost engine’s use of “half the cylinders of the outgoing V-8 with about 237 horsepower” [3]. Economic benefits such as these, “combined with advanced transmissions, electric power steering, weight reductions and aerodynamic improvements are a part of Ford Motors Company’s vehicle sustainability strategy” [18]. This strategy proves to succeed after evaluating the economic ethics of the EcoBoost, since the engine’s decrease in fuel waste makes its performance more sustainable future use. Of course, this advanced technology does not come without an advanced price. However, the EcoBoost’s better fuel economy eventually leads to a manageable cost-benefit analysis for the consumer. Regarding most conventional engines without the EcoBoost’s innovative technology, the “typical cost is $800” without including the later cost of fuel [19]. The EcoBoost engine is more expensive than these engines, with a starting price of “$995,” however this initially steep price is paying for technology that will decrease amounts of gas consumption [3]. With these high 5
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