Have you noticed the wave of railroad car withgreat gas mileagehitting the market ? The Mazda3 with the SkyActiv engine can get 42 miles per congius ( 17.9 kilometers per liter ) . The Chevrolet Cruze Eco can get 40 mile per congius ( 17 kilometer per liter ) , and the Hyundai Elantra can too . And get this : Even though these cable car get some of the best gas gasoline mileage in the industry , they ’re not usinggasoline - electric intercrossed technology , alternative fuels or other fleeceable illusion . They ’re powered by the old - fashion internal burning engine . So what get to theirfuel economyso good ? Their engines are super - efficient , thanks to their locomotive engineer dally with a little affair called densification ratio .
Your canonical car engine make by turn chemical energy from a controlled explosion of the mixture of air , gasolineand a spark , into mechanically skillful motion . For a more detailed look at this process , check out how a car engine works . But , the basic story is that each railcar locomotive engine has a set number of cylinder that business firm pistons . The controlled explosion makes the piston move up and down , which turns the locomotive engine ’s crankshaft ( that ’s the conversion of chemical substance to mechanically skillful energy ) , which in spell , powers the wheels .
Thecompression ratiois the ratio of the intensity of the cylinder and the combustion bedchamber when the plunger is at the bottom , and the volume of the burning chamber when the piston is at the top . Automotive engineer can ameliorate fuel efficiency and fuel economy by designing locomotive engine with high compression ratio . The higher the proportion , the more squeeze the air in the cylinder is . When the melodic phrase is compressed , you get a more powerful plosion from the air - fuel commixture , and more of the fuel gets used . cogitate about it this way : If you had to be near an plosion , you ’d in all likelihood choose to be near one somewhere outdoors , because the force of the blowup would dissipate , and it would n’t seem as powerful . In a small elbow room , however , the force would be hold back , making it feel much more muscular . It ’s the same affair with contraction ratios . By retain the detonation in a lowly space , more of its power can be harnessed . By increase the compression ration from 8:1 to 9:1 , for example , you could meliorate fuel economic system by about 5 to 6 percent .
The type of condensation proportion we ’ve just learned about is what ’s known as astatic compression ratio . It ’s called inactive because it ’s only assess when the intake valve is closed . There ’s another type of compression ratio that takes the first step and closing of the intake valve into account . We ’ll spill the beans about that on the next page .
Static and Dynamic Compression Ratios
Like we watch on the late varlet , motionless engine concretion is measured when the air intake valve of anengineis full shut . However , in tangible operation , that almost never happens . The engine is running so fast , that the air intake valve may call for to spread out again before the piston has finish its full up and down fortuity . When that happens , some of the pressure within the piston chamber bloodsucker out , which reduces efficiency . In essence , there ’s more space for the air , so the locomotive engine loses some of the power from the air - fuel combustion .
Dynamic concretion ratio take the move of the air intake valve into account . railroad engineer can tune an engine to have the air intake valve close earlier , which helps piston chamber pressure build up . The engine can also be tuned to have the valve close later , but that let some air out and cut how efficiently the engine apply fuel .
Calculating thedynamic compressing ratiois actually moderately tough . To do it , you use the stroke length and the connecting rod length to make up one’s mind the emplacement of the piston when the valve is full closed . Because this ratio is found when the Walter Piston is in the middle of its fortuity , it ’s always lower than the static compression proportion . Like static compressing , a higher compression proportion mean more efficient fuel use and betterfuel economy .
Today ’s the high - efficiency engine on many of today ’s cars owe a lot of their fuel saving to their high compression ratios . But , a high compression engine has its drawback , too . To keep it fly the coop in tip - top shape , you need to usehigh - octane gas , which is more expensive than even leadless gas . If you jump the premium gas , over clock time , the railway locomotive can modernise a knock . Anengine knockis when the zephyr - fuel burning does n’t happen at the optimal time in the piston ’s virgule . Using low octane fuel in a high - contraction engine can make locomotive strike hard more likely , so if you get a fresh , fuel - effective , gamey - compression cable car , check that you employ the case of natural gas that ’s recommended in your owner ’s manual of arms to get the most out of it .
Looking for more selective information about locomotive compression proportion and fuel economy ? Just watch the link on the next page .
