Why a diesel engine is usually more efficient than a spark ignition engine?

Why a diesel engine is usually more efficient than a spark ignition engine?

A diesel engine is usually more efficient than a spark ignition engine because the compression ratio of diesel engine is higher than petrol engine. Therefore fuel is injected to compressed air and hence air fuel mixture is heterogeneous.

What is the advantage of spark ignition engines vs compression ignition engines?

6… Thermal efficiency: Due to lower compression ratio, maximum value of thermal efficiency is lower in an S.I engine compared to that of C.I. 7… Weight : S.I engines are generally lighter in weight due to their lower peak pressures as compare to C.I engines that are generally heavier, due to higher peak pressure.

What are the air fuel requirements for a spark ignition engine at different operating conditions?

Engine Air-fuel Ratios The best fuel economy is obtained with a 15:1 to 16:1 ratio, while maximum power output is achieved with a 12.5:1 to 13.5:1 ratio. A rich mixture in the order of 11:1 is required for idle heavy load, and high-speed conditions.

What is the main practical limitation on the compression ratio of a spark ignition engine and a compression ignition engine?

Spark ignition (SI) engines The compression ratio is limited by the autoignition of the fuel–air mixture ahead of the flame so as not to cause combustion knock.

How is the fuel ignited in a diesel engine?

Injected fuel is ignited by its reaction to compressed hot air in the cylinder, a more efficient process than that of the spark-ignition internal-combustion engine. The diesel engine gains its energy by burning fuel injected or sprayed into the compressed, hot air charge within the cylinder.

Which is more efficient Otto or Diesel?

Explanation: Otto cycle is more efficient than Diesel cycle for a given compression ratio. For constant maximum pressure and heat input, the air standard efficiency of the gas power cycle is in the order.

What is the difference between spark ignition Andcompression ignition engines?

The Spark Ignition (SI) engine, as its name indicates uses spark to ignite the fuel. And in Compression Ignition (CI) engine, the air is compressed within the cylinder and the heat of this compression air is used to ignite the fuel.

Why does idling require a rich mixture?

The mass of exhaust gases in the cylinder at the end of exhaust stroke remains fairly constant throughout the idling range. Thus, the engine requires a rich mixture (more fuel than a stoichiometric mixture) for starting at idling to compensate for the charge dilution due to exhaust gases from the combustion chamber.

Why are high compression ratios not used in spark ignition engines?

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.

What is the air to fuel ratio for a lean burn engine?

The air / fuel ratio needed to stoichiometrically combust gasoline, by contrast, is 14.64:1. The excess of air in a lean-burn engine emits far less hydrocarbons. High air–fuel ratios can also be used to reduce losses caused by other engine power management systems such as throttling losses.

What is a compression ignition engine?

Compression ignition engines are used in a variety of commercial and consumer applications around the world, powering devices like large ships, locomotives, commercial trucks, construction and farm equipment, power generators, and even automobiles. Almost exclusively, these applications utilize diesel fuel for combustion.

Why is there no throttling in spark ignition engines?

In addition, the compression ignition needed no throttling to control the power output of the engine. Direct injection of the fuel into the combustion chamber provided high resistance to knock, which limits the compression ratio and ultimately, the efficiency of spark ignition engines.

What are the advantages of lean burning engines?

The engines designed for lean-burning can employ higher compression ratios and thus provide better performance, efficient fuel use and low exhaust hydrocarbon emissions than those found in conventional gasoline engines. Ultra lean mixtures with very high air–fuel ratios can only be achieved by direct injection engines.