During process 2-3
the fuel is injected and combusted
and this is represented by a constant pressure expansion process. At state 3 (“fuel cutoff”) the expansion process continues adiabatically with the temperature decreasing until the expansion is complete.
What is the compression ratio for diesel engine?
Diesel engines are typically constructed with compression ratios in the range
14:1 to 22:1
.
What is diesel cycle with diagram?
| S.no Process Operation | 1. 1-2: Isentropic compression Compression of air. | 2. 2-3: Constant Pressure heat addition Heat is added from an external source (hot body) | 3. 3-4: Isentropic expansion Expansion of air takes place due to heat addition. | 4. 4-1: Constant volume heat rejection Heat is rejected to a sink. |
|---|
What type of cycle is a diesel cycle?
Diesel cycle is
one of the most common thermodynamic cycles
found in automobile engines and describes the functioning of a typical compression ignition piston engine. Because of the high temperature developed during the adiabatic compression, the fuel spontaneously ignites as it is injected.
What is the cutoff ratio?
The cutoff ratio is
the ratio of the volume after combustion to the volume before combustion
.
How do you calculate the efficiency of a diesel cycle?
- η
Diesel
is the maximum thermal efficiency of a Diesel cycle. - α is the cut-off ratio V
3
/V
2
(i.e., the ratio of volumes at the end and start of the combustion phase) - CR is the compression ratio.
- κ = c
p
/c
v
= 1.4.
Why compression ratio of diesel engine is higher?
Diesel engines use direct fuel injection i.e. diesel fuel is injected directly into the cylinder.
A diesel engine compresses only air
, so the compression ratio can be much higher. The higher the compression ratio, the more power generated.
How does a 2 cycle diesel work?
What happens if compression ratio is too high?
Higher compression ratios
can make gasoline (petrol) engines subject to engine knocking
(also known as “detonation”, “pre-ignition” or “pinging”) if lower octane-rated fuel is used. This can reduce efficiency or damage the engine if knock sensors are not present to modify the ignition timing.
How many processes are there in a diesel cycle?
The idealized Diesel cycle assumes an ideal gas and ignores combustion chemistry, exhaust- and recharge procedures and simply follows
four distinct processes
: 1→2 : isentropic compression of the fluid (blue) 2→3 : reversible constant pressure heating (red) 3→4 : isentropic expansion (yellow)
What is Otto and Diesel cycle?
Otto cycle is used for petrol or spark ignition engine while diesel cycle is used for diesel or compression ignition engine
. The main difference between Otto cycle and Diesel cycle is that in Otto cycle heat addition takes place at constant volume and in diesel cycle heat addition takes places at constant pressure.
What is PV and TS diagram?
As described on the work slide,
the area under a process curve on a p-V diagram is equal to the work performed by a gas during the process
. On the right of the figure we have plotted the temperature versus the entropy of the gas. This plot is called a T-s diagram.
What do you mean by Diesel cycle?
Definition of diesel cycle
:
an ideal-engine cycle during which the working substance successively undergoes adiabatic compression, constant-pressure heating, adiabatic expansion, and constant-volume cooling
— compare diesel engine, otto cycle.
Which is more efficient Otto or Diesel cycle?
Although for a given compression ratio the
Otto cycle
has higher efficiency, because the Diesel engine can be operated to higher compression ratio, the engine can actually have higher efficiency than an Otto cycle when both are operated at compression ratios that might be achieved in practice.
How efficient is a diesel engine?
What is the maximum efficiency an engine can achieve? The diesel engine has a theoretical system efficiency of
between 55-60%
. For reference, the best power stations operate at 50-55% efficiency, and fuel cells are also around 50%+ efficient – so diesel engines can be incredible efficient.
How do you cut off a diesel engine?
The engine can be shut down by
restricting the fuel return at the injection pump
. Since the engine needs air to run choking the air supply will also kill the engine. You can remove the mushroom cap air intake and put a piece of wood over the top to stop the air.
Why do diesel engines not need spark plugs?
The higher the ratio, the more air is compressed, and more of the injected fuel is ignited during combustion. The result is a more powerful explosion and better performance. While
compression ignition
means that diesels don’t require spark plugs, they can come fitted with components called glow plugs.
What is a good compression ratio?
Compression ratios usually vary between 1.05–7 per stage; however, a ratio of
3.5–4.0 per stage
is considered maximum for most process operations. Quite often, the temperature rise of the gas during the compression dictates a limit for the safe or reasonable pressure rise.
Does higher compression require more fuel?
All things equal,
engines with higher compression ratios require higher fuel octane
. This is because a lower octane fuel may begin to ignite prior to the initiation of the spark event through the ignition system, a condition known as detonation or auto ignition.
Are diesels 2-stroke or 4-stroke?
More on 2-stroke engines below. Diesel engines are
4-stroke
, but they differ from their gasoline-powered counterparts in their method of combustion. Diesels rely on very high compression ratios to ignite the air/fuel mixture rather than a spark plug.
Do 2-stroke diesels need oil?
Two stroke diesel engines
do not require a fuel-oil mixture
, nor do they rely on fuel for lubrication; they feature a conventional crankcase filled with engine oil.
Are all Detroit Diesels 2-stroke?
| Series 71 | Configuration Multi-cylinder, inline and V-type | Displacement 71 cu in (1.2 L) (per cylinder) | Cylinder bore 41⁄4 in (108 mm) | Piston stroke 5 in (127 mm) |
|---|
