How is thermal efficiency of Otto cycle calculated?
When we rewrite the expression for thermal efficiency using the compression ratio, we conclude the air-standard Otto cycle thermal efficiency is a function of compression ratio and κ = cp/cv.
What is the formula for compression ratio of the Otto cycle?
For example, let assume an Otto cycle with compression ratio of CR = 10 : 1. The volume of the chamber is 500 cm³ = 500×10-6 m3 (0.5l) prior to the compression stroke. For this engine all required volumes are known: V1 = V4 = Vmax = 500×10-6 m3 (0.5l)
How is compression ratio calculated?
Compression ratio formula It can be calculated according to the cylinder volume formula: Vd = b2 * s * π / 4 . Vc is the volume above the piston when the piston is at the top dead-centre (its topmost position), also called the compressed volume. b is the cylinder bore (diameter). s is the piston stroke length.
Can you have too much octane?
The higher the octane rating, the slower and colder the fuel burns. If you run too much octane in your engine it won’t run very well because the burn is way too slow. If the octane is too low, the fuel will burn too fast and too hot which causes detonation and leads to sure-fire engine damage.
Which engine operates at higher compression ratios?
CI engines can run at higher compression ratios since they are based on the autoignition principle and are not limited by the premixed fuel–air combustion knock in SI engines. CI engines achieve higher efficiencies than SI engines, peaking around 45% (US DOE, 2010).
What happens when compression ratio is increased?
The thermal efficiency increases and the brake specific fuel consumption decreases with the increase of compression ratio. The higher compression ratio results in higher in-cylinder pressure and higher heat release rate as well as lower ignition delay.
How do I lower my compression ratio?
A thicker gasket will reduce the compression ratio by a small fraction, probably only by . 1 or . 2. This is by far the easiest method of reducing compression but the risk is that you are more prone to head gasket failure and the gains in lower compression are minimal.
Does compression ratio affect fuel economy?
Automotive engineers can improve fuel efficiency and fuel economy by designing engines with high compression ratios. The higher the ratio, the more compressed the air in the cylinder is. When the air is compressed, you get a more powerful explosion from the air-fuel mixture, and more of the fuel gets used.
What are the three main reasons for high fuel efficiency in diesel engines?
The diesel thermodynamic cycle efficiency advantage over the more common spark-ignition (SI) gasoline engine stems from three major factors: the diesel engine’s use of lean mixtures, its lack of need for throttling the intake charge, and its higher compression ratios.
How does compression ratio affect performance?
An increase in compression ratio results in better mixing of fuel and higher temperature during the compression stroke. The increase in the compression ratio is expected to result in rise in cylinder pressure. This leads to reduced ignition delay and the combustion occurs near the TDC.