Looking at the bsfc maps posted by drivbiwire you can see the prius engine is operated so its bsfc is about 230 gkwhr. For those who dont know, the prius uses an atkinson cycle combustion engine, combined with the electric motor, to provide power. The disadvantage of the fourstroke atkinsoncycle engine versus the more common ottocycle engine is reduced power density. Aug 04, 2016 the atkinson cycle is ideal for hybrids because their electric motors make up for the lost lowspeed output. Worth noting that the prius engine only simulates the atkinson cycle by holding the intake valve open past bdc, allowing some of the air to be forced back into the intake track. The purpose is to effectively increase the expansion ratio on the power stroke and thus increase delivered efficiency.
The atkinson cycle delays the intake valves closing until the piston has completed 20 to 30 percent of its upward travel on the compression stroke. The key advantage is higher efficiency than is achievable in an otto engine, albeit with some loss of lowspeed output. The atkinson cycle is designed to provide higher efficiency at the expense of power density. It was proven that the atkinson cycle offers higher efficiency at partload conditions compared to the otto cycle. That extra force is essentially wasted energy, the atkinson. In the otto cycle, some of the force during the power stroke goes to pushing the piston down, but more force is produced than needed. The atkinson cycle uses a different thermodynamic process than the traditional otto cycle common to most gasoline engines. In an earlier thread it was mentioned that the atkinson combustion cycle changes over to otto at some point. What is the difference between the atkinson and otto cycles. The most common combustion engine these days is a fourstroke otto cycle engine, where a piston goes up and down inside a cylinder and a spark ignites a mixture of gas and air. The atkinson cycle is more efficient than the otto cycle, so the 2016 tacomas new engine will offer better fuel economy than other conventional v6 engines turns out this isnt true.
And unless i understand the atkinson cycle incorrectly, an otto cycle will produce more power than an atkinson cycle. The cycle on which most of our cars run is the otto cycle. Compression and expansion ratios are the same in an otto engine. Brian cooley discusses the technology and why its becoming a. Further it is to be noted that heat rejection occurs at lower average temperature t. In fact if you read about the original atkinson engine then you will find it is a totally different t. In an otto cycle engine, this is done in two rotations of the crankshaft. An atkinson cycle engine makes less power than the otherwise equivalent otto cycle unit, which is why the design is more popular with hybrid models, which aim for fuel economy over acceleration. Heres a nifty animation of a motor using the original atkinson cycle or near enough.
We all know that an engine, piston or rotor, needs to complete a cycle to make and deliver power. The otto atkinson cycle engine operates on the otto cycle at full load, for good power density, and on the atkinson cycle at part loads, for reduced fuel consumption. Funny, i always thought the miller cycle came from engine builder harry miller. The idea of the atkinson cycle is to get more work than that given by otto cycle. Ciclo otto vs ciclo atkinson vs ciclo miller youtube. The atkinson cycle and improving the ices efficiency. Otto cycle engine an overview sciencedirect topics. And to counter that, electric motors are used to give an initial push until the cycle can be used. In fact the atkinson cycle is at its most efficient when used with a supercharger or hybrid motor.
I can only describe atkinson cycle on basis of toyotalexus technologies, as different manufacturers use a bit different tecniques at this point. As wikipedia says, its a simulated atkinson cycle and really a modified otto cycle engine. Comparison of performances of airstandard atkinson, diesel and otto cycles with constant specific heats. What is the difference between the atkinson and otto. Same goes for an atkinson cycle engine, so heres a quick refresher of the process. The complete redesign has given the toyota tacoma a bolder, more dominant platform that is matched by a more powerful, more efficient atkinson cycle engine. Jan 14, 2015 this revelation allowed toyota to build the worlds first otto cycle engine with a simulated atkinsontype valve action to significantly improve fuel efficiency. The atkinson cycle was designed and built by james atkinson in 1882, the diesel cycle was invented by rudolph diesel in 1893 and the otto cycle. This wikipedia animation shows the complexity perfectly. The atkinson cycle was designed and built by james atkinson in 1882, the diesel cycle was invented by rudolph diesel in. Due to a smaller portion of the compression stroke being devoted to compressing the intake air, an atkinson cycle engine does not take in as much air as would a similarly designed and sized otto cycle engine. Is it because of production costs or some other reason. The atkinson and miller cycle engines not exactly what. The atkinson cycle is ideal for hybrids because their electric motor s make.
The atkinson cycle uses a different thermodynamic process than the traditional. Fourstroke engines have four separate phases within. The atkinson cycle engine in the prius has the advantage of being operated to maximize its thermal efficiency. There are several notable differences that orignally allowed mr. The atkinson cycle is a method of internal combustion first proposed by english engineer, james atkinson, in 1882. This was achieved by use of variable engine strokes from a complex crankshaft. Named after its inventor, the atkinson engine differs from other combustion engines where efficiency is emphasized over. The basic difference between the atkinson cycle and the otto cycle, is that during the compression stroke, the intake valve is left open for a. The advantage of the atkinson cycle is that it is much more efficient than the otto. The atkinson cycle and improving the ices efficiency claytex. The effects of input temperature and compression ratio on the net output work and efficiency of the atkinson cycle, diesel cycle and otto cycle are analyzed. This leads to more thermal efficiency as more heat is extracted which, otherwise, would have got wasted in exhaust. The atkinson cycle is a method of internal combustion first proposed by english. In this blog post, an engine and its components are modelled in dymola to execute a comparison between the otto and atkinson cycles.
It is the idealized thermodynamic cycle utilized by most spark ignition systems. With an auto if it has low load it will be low rpm. The atkinson cycle engine is a type of internal combustion engine, which was designed and built by james atkinson in 1882 1. This revelation allowed toyota to build the worlds first otto cycle engine with a simulated atkinson type valve action to significantly improve fuel efficiency. How an atkinson cycle engine works auto howstuffworks. Is it possible im feeling the change over from atkinson cycle to otto. Mar 28, 2019 the atkinson cycle is a modified otto cycle in which the intake valves are held open for a portion of the compression stroke. In the original atkinson engine, the inventor added a couple of linkages so that all four strokes could be completed with a single rotation of the crankshaft. The atkinson cycle engine may be under your cars hood and youd never know. Jul 14, 2010 the otto cycle engine design has dominated since the beginning of vehicle construction but now the atkinson cycle, or a modified concept of it is making a comeback in todays hybrid vehicles. To work around ottos patent the wacky linkage wouldnt have been enough by itself, since it didnt actually improve anything.
An atkinson cycle has a greater work output and a higher thermal efficiency than the otto cycle at the same operating condition. Aug 31, 2016 today we will discuss about difference between diesel cycle vs otto cycle. Jan 22, 2015 patented in 1882 by british engineer james atkinson, the atkinson cycle significantly improved the fuelefficiency of a fourstroke spark ignition engine through one particularly ingenious modification. The atkinson design uses the four strokes of the otto cycle to complete the combustion process, but unlike the otto cycle, atkinson s late closing of the intake valves produces an effective. Comparison of performances of air standard atkinson and otto.
Difference between otto cycle and diesel cycle mechanical. Mar 18, 2017 the atkinson cycle is used extensively in hybrid cars such as the toyota prius as it uses less fuel than the otto cycle. Thermal efficiency for atkinson cycle nuclear power. Jul 22, 2016 the atkinson cycle is a method of internal combustion first proposed by english engineer, james atkinson, in 1882.
Brian cooley discusses the technology and why its becoming a mainstay in late model, efficient cars. The real workflow in real engines used in practice to this day it is suggested by ralph miller. When full power is so seldom needed as when eco driving a car, optimizing for power is a waste when it comes to fuel efficiency. The ottoatkinson cycle enginefuel economy and emissions. This is achieved by increasing the geometric compression ratio and employing late intake valve closing. In this configuration, an increase in both power and efficiency can be achieved when compared to the otto. Why is this the case, and what is the difference between these two cycles. And finally, talking of heat loss from the otto and atkinson engines, companies like bmw are looking at using some of the heat. With this vision, this blog post has the aim of clarifying the advantages and disadvantages of the atkinson cycle using dymola software as a design, test, and validation tool. Atkinson and miller cycle engines are dieal as hybrid. Redesigned from top to bottom, the reinvigorated 2016 toyota tacoma is more powerful and more efficient than ever. Atkinson, diesel and otto cycles are three types of fourstroke engines. Apr 16, 2018 atkinson cycle is an ideal cycle for otto engine exhausting to a gas turbine. What is the atkinson combustion cycle, and what are its.
Petrol engines work on otto cycle and diesel engines work on diesel cycle. Both these cycle are air standard cycles of automobile engines. The atkinson cycle is used extensively in hybrid cars such as the toyota prius as it uses less fuel than the otto cycle. In this paper, the investigations of atkinson cycle converted from conventional otto cycle gasoline engine have been carried out. The actual atkinson design was far more rube goldberg. These engines are generally found on hybrid electric vehicles, where efficiency is the goal, and the power lost compared to the miller cycle is made up through the use of electric motors. By and large, the miller atkinson cycle is not an independent cycle, but a variety of known thermodynamic otto and diesel cycles.
To understand the atkinson cycle, it is easier if we first look at the otto cycle and then compare differences. I like the atkinson story as a case of patents stimulating innovation. In this paper, the effects of heat transfer on the net output work and the indicated thermal efficiency of an air standard atkinson cycle are analyzed. Comparison of performances of air standard atkinson. Could you please explain why the atkinson cycle inline four is more popular than the flat four horizontally opposed boxer engine. This reduces the compression ratio, but the subsequent expansion ratio is unchanged. Well you are probably right because an atkinson cycle produces about 30% less power than an otto cycle. The most common combustion engine these days is a fourstroke otto cycle engine, where a piston goes up and down inside a cylinder and a spark ignites a. In 1882, a british engineer, james atkinson advanced the study of heat engines by inventing of several heat engines that have an increased efficiency over the otto cycle. Today, the term atkinson cycle is used to describe millers modified fourstroke otto cycle, in which the intake valve is held open longer than normal to allow the piston to push some of the intake air back out of the cylinder. Atkinson cycle which is the required equation for air standard efficiency of the cycle.
In an atkinson cycle engine, the intake valve remains open during the beginning of the compression stroke. The atkinson cycle relies upon many of the same principles as the otto cycle. Aug 06, 2015 the otto cycle was given by german scientist otto, in 1876 and diesel cycle was discovered by dr. Atkinson is the author of the abstract idea of the engine with a physically different compression and expansion strokes. The otto cycle engine design has dominated since the beginning of vehicle construction but now the atkinson cycle, or a modified concept of it is making a comeback in todays hybrid vehicles. Comparison of airstandard atkinson, diesel and otto. Due to a smaller portion of the compression stroke being devoted to compressing the intake air, an atkinsoncycle engine does not take in as much air as would a similarly designed and sized ottocycle engine. The advantage of the atkinson cycle is that it is much more efficient than the otto cycle. In otto cycle engines, the pressure in the cylinder at the end of the expansion power stroke is still 3 to 5 atm when the exhaust valve opens.
As a result, some of the fresh charge is driven back into the intake manifold by the rising piston so the cylinder is. The downside to the atkinson cycle is that it has low torque output compared to the otto cycle, so it has been largely disregarded as an internal combustion. It was developed by james atkinson as a workaround for the patents that otto had on traditional fourstroke engines. Besides the diesel and spark ignition internal combustion engine currently being used, there is another type of engine that was introduced more than a hundred year ago which now gains favor in hybrid electric application. A similar delayed valveclosing method is used in some modern versions of atkinson cycle engines, but without the supercharging. It is assumed that the compression and power processes are isentropic. While an otto cycle engine modified to run on the atkinson cycle provides. The original atkinson cycle engine of 1887 used a complex system of rods and journals to make the expansion power stroke longer than the compression stroke, achieving greater thermal efficiency than a normal fourstroke, otto cycle engine. But what are the differences and how they operate, lets take a look.
So he comes up with the atkinson cycle improvement. Feb 28, 2008 because the expansion power stroke, as well as the intake stroke are both of the order of 15. This is achieved by increasing the geometric compression rati. Get an indepth look at toyotas new 2grfks v6 atkinson cycle engine. The atkinson cycle has a larger expansion ratio than compression ratio. In an atkinson cycle modified otto cycle, the system executing the cycle undergoes a series of four processes. Ever since engines were installed in carriages there has been an ongoing discussion among automotive enthusiasts about the merits of the steam engine rankine cycle powered carriage over the internal combustion engine otto cycle powered carriage.
Toyota makes its atkinson cycle engine stop in mid compression cycle to help in the startup next time when you turn the engine on. The disadvantage of the fourstroke atkinson cycle engine versus the more common otto cycle engine is reduced power density. A miller cycle engine leaves the intake valve open during part of the compression stroke, so that the. Atkinson, diesel and otto cycles with constant specific heats of working fluid. Of the two engines, the atkinson is the more significantly changed.
The power output would be lower in atkinson cycle engine as compared to a similar sized otto cycle engine. The clever arrangement of levers allows the atkinson engine to cycle the piston through all four strokes in only one revolution of the main crankshaft, and allows the strokes to be different lengths. The disadvangtage is that it has less power especially when moving the car from a dead stop. The way i look at the atkinson cycle is that in the normal otto cycle there is still quite a lot of energy left in the compressed gases when the exhaust valve opens. The main point is to get more fuel efficiency at the expense of power density. Atkinson cycle has a larger expansion ratio than compression ratio.
In otto cycle the heat addition is takes place at constant volume where as in diesel cycle heat is added at constant pressure. The atkinson cycle is a modified otto cycle in which the intake valves are held open for a portion of the compression stroke. Ottos engine, inlcuding the longer power stroke vs. Oct 06, 2015 the atkinson cycle engine may be under your cars hood and youd never know. They could push the piston further and release more energy from the burn. A miller cycle engine is very similar to an otto cycle engine.
The british engineer james atkinson 18461914 realized that the efficiency of the otto cycle could be improved if the combustion gases could be expanded to near atmospheric pressure before being exhausted from the engine. Comparison of performances of air standard atkinson and. The atkinson cycle is much different from the typical otto cycle that is found in most internal combustion engine ice cars today. The miller cycle uses pistons, valves, a spark plug, etc. My rav 4 awd hybrid is delivering 41 mpg in the city and on the. What is the atkinson combustion cycle, and what are its benefits. Comparisons of the performances of air standard atkinson and otto cycles with heat transfer considerations are also discussed. The four basic phases of the otto cycle remained but atkinson introduced a new timing sequence to delay the closing of the intake valve during. The atkinson engine is essentially an otto four stroke engine with a different means of linking the piston to the crankshaft. Apparently, the atkinson cycle and miller cycle names are not trademarked since neither is true to its original patents when it comes modern otto engines. Pdf comparison of performances of airstandard atkinson. Comparison of performances of air standard atkinson, diesel. First of all, high geometry compression ratio cr has been optimized through piston redesign from 10. Hybrids like the prius use atkinson cycle to power their internal combustion engines.
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