CI-DI I C Engines for Automobiles P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Introduction of All the Fuel Inside is not Safe too…..

Rudolf Christian Karl Diesel Diesel published a treatise entitled, Theory and Construction of a Rational Heat-engine to Replace the Steam Engine and Combustion Engines Known Today. This formed the basis for his work on and invention of, the diesel engine. In his engine, fuel was injected at the end of compression and the fuel was ignited by the high temperature resulting from compression.

Diesel’s Direct Injection CI Engine Typical SI engines 9 < r < 11 k = 1.4

Schematic of Spray Dynamics in Diesel Engine

Why Is It Happening?

Components of Entropy generation mechanisms in CI engines The Global Entropy generation contains the following sub-processes: Spray development Air entrainment and mixing Droplet evaporation Auto Ignition Combustion and thermodynamic Processes Heat transfer among various parts (Zones) of Cylinder Particulates & NOx formation, Variation of gas properties Variation of Chemical compositions

Sauter Mean Diameter The representative diameter is defined as Sauter mean diameter (SMD). Introducing the definition of SMD:

is the liquid surface tension, L is the liquid viscosity, Where is the liquid surface tension, L is the liquid viscosity, A is the air density,  L is the liquid density, pL, is the injection pressure differential across the nozzle, is the half spray angle and t is the film thickness, given by where do is the discharge orifice diameter and FN is the nozzle flow number defined by

Droplet evaporation Fuel–air mixing is the key factor for in-cylinder combustion at high loads. As the engine load decrease, the process of droplet evaporation becomes more important. It is dominant under starting conditions. The droplet evaporation is calculated with the theory of single droplet. The fuel spray on break-up atomizes to a very large number of droplets. The droplet size distribution in sprays is the crucial parameter needed for the fundamental analysis of therate of evaporation.

where  is the evaporation constant for forced convection. Spray vaporization The spray is divided into an initial "cool” and "hot" zone. Within the cool zone, heat transfer is restricted to radiation from the flame front to the droplet surface. In the hot zone, heat transfer takes place both by radiation from the flame front and by turbulent convection. The reduction in droplet diameter due to vaporization follows the "d2 law": where  is the evaporation constant for forced convection.

The evaporation in Forced convection The evaporation constant in forced convection Where, k is the thermal conductivity of the gas, Cp is the specific heat of the gas, f is the density of the fuel and B=the transfer number

hfg = latent heat of vaporization per unit mass of fuel, T= temperature of gas surrounding the droplet, Tf= temperature of drop surface, Q = heat of reaction, Y0=mass fraction of oxidant in the surrounding atmosphere and  stoichiometric mixture ratio.

A, B and n are experimental constants. Ignition Delay The sum of times required for sub process. The most widely reported correlation relating the ignition delay to the ambient gas condition is given by the relation where τ is the ignition delay, Pg and Tg are the ambient gas mean pressure and temperature before autoignition takes place, A, B and n are experimental constants.

Arhenius-type equation for Ignition Delay An Arhenius type equation for Ignition delay is: p :Premixed air fuel ratio.

Symptoms to be Sensed to Predict Auto Ignition

Effect of Gas Temperature on Ignition Delay

Effect of Equivalence Ratio on Ignition Delay

The flammability limits versus the number of carbon atoms in alkanes

Temporal Evolutions of Combustion in CI Engine

Direct injection (DI) diesel spray: Spatial distribution

Spatial Variations in CI Engines

Temporal evolution of Combustion in Each Zone Start of injection End of injecction -20 -10 TC 10 20 30

Experimental Study of Combustion Process In above Eq., the rate of the heat loss Qloss/dθ is expressed as: The convective heat transfer coefficient is given by the Woschni model as For combustion and expansion processes: C1=0.00324.

In-cylinder Processes in a Diesel Engine

Dangerous Emissions in CI Engine