There are two main limiting factors on how high an engine’s compression ratio can be. The first is that the loads on the piston, rod and crank get too high , as a result of the increased combustion pressure. The second is the detonation limit of the fuel used.
What determines compression ratio?
Selecting the Power Plant
The compression ratio is defined as the ratio between the volume of the cylinder with the piston in the bottom position, V bottom (largest volume) , and in the top position, V top (smallest volume). The higher this ratio, the greater will be the power output from a given engine.
What limits the compression ratio in the Otto cycle?
The unburned mixture may autoignite by detonating from pressure and heat alone, rather than ignite from the spark plug at exactly the right time. The engine knocking can be reduced by using high-octane fuel, which increases the gasoline’s resistance to autoignition.
Why high compression ratios are not recommended for Otto cycle?
(1) With high compression ratio, they operate at higher pressures and offer a cleaner and complete burn of fuel leading to better mileages too. However, it’s not ALL good. The higher pressure requires stronger build of the engine (in some cases heavier). Chances of knocking in the engine are higher.
What will be the effect on the efficiency of an Otto cycle having a compression ratio of 8 if CV increases by 1.6 %?
what will be the effect on the efficiency of an Otto Cycle having compression ratio 8, if C V increases by 1.6% C V , specific heat? Otto cycle efficiency is given by, ... Therefore there is decrease in 1.026 % of efficiency with increase in 1.6 % specific heat at constant volume .
What octane is needed for 11 1 compression?
95 Octane . Gasoline with this octane number is known in Indonesia under the brands Pertamax Plus (produced by Pertamina), Super Extra (produced by Shell), and Primax (produced by Petronas). This type of gasoline is advisable for car engines with compression ratios of 11:1 to 12:1.
What engine has highest compression ratio?
- Cars built from 1955–1972 which were designed for high-octane leaded gasoline, which allowed compression ratios up to 13∶1.
- Some Mazda SkyActiv engines released since 2012 have compression ratios up to 14∶1.
Does higher compression increase torque?
Much like increased engine displacement, higher compression ratios are a sure path to increased torque . ... Many street engine combinations running a big cam for top-end power experience a significant loss of low-end torque. This occurs because the intake valves close much later when the piston is farther up the bore.
What is the highest compression ratio for 93 octane?
Don’t worry about anything from 91-93 octane, stay with 11.5-1 and under .
Does higher compression increase horsepower?
Increasing compression is the most productive way to increase horsepower . Build compression into your engine and you build in power. In more than a century of internal combustion, there has never been a more common sense way to make power.
What is K in Otto cycle?
Thermal Efficiency Derivation
A typical value for an air/fuel mixture is k = 1.35 .
Do high compression engines run hotter?
Yes, when air is compressed it creates heat. In referance to the original question, yes higher compression does cause more heat on the compression stroke but the real heat is caused by the extra power assocaited with high compression engines. That’s why the turbocharged guys like to run intercoolers.
What is constant in Otto cycle?
Otto cycle Thermodynamics. 1. an ideal thermodynamic combustion cycle, as follows: a compression at constant entropy ; a constant-volume heat transfer to the system; an expansion at constant entropy; and a constant-volume heat transfer from the system.
Which cycle is more efficient with respect to the same compression ratio?
Explanation: Otto cycle is more efficient than Diesel cycle for a given compression ratio. 6. For constant maximum pressure and heat input, the air standard efficiency of the gas power cycle is in the order.
What is the formula for compression RK ratio of the Otto cycle?
Explanation: This is the expression for efficiency of Otto cycle and rk= compression ratio=Vmax/Vmin.
What is the formula for compression R ratio of the Otto cycle?
Process 1–2 compression stroke (B on diagrams)
Piston moves from crank end (BDC, bottom dead centre and maximum volume) to cylinder head end (TDC, top dead centre and minimum volume) as the working gas with initial state 1 is compressed isentropically to state point 2, through compression ratio (V 1 /V 2 ) .
