You can make a reasonably accurate estimation by applying the First Law of thermodynamics, and assuming that the process within the cylinder is adiabatic. The equation that you should use is the following:

W= ΔH

Where, W is the gross work output of the cycle in the cylinder (excluding mechanical losses), and ΔH is the enthalpy variation between the reactants (air + fuel) and the products including excess air. You can then convert the enthalpy values at the valve outlet to temperature values by using termochemical tables: https://janaf.nist.gov/

As an example, the energy balace for a simple reaction with stoichiometric oxygen mixture with methane is done as follows:

1. First you write the reaction

CH4+2O2->CO2+2H2O

2. Then you calculate the enthalpy of the reactants (in moles)

Hreact=1·hCH4+2·hO2

3. Then you calculate the enthalpy of the products (consider that the work W has a negative value)

Hprod=W+Hreact

4. Finally, you convert the enthalpy of the products to temperature by using the termochemical tables. You might need to do several iterations, and an interpolation, until the sum of the enthalpies of the products matches the value of Hprod:

Hprod=1·hCO2+2·hH2O

You may find the theoretical calculations for ICE in any thermodynamics textbook. However, there are several losses that need to be considered when applying theoretical thermodynamics analysis: incomplete combustion, heat transfer losses in connections, etc.

Heat balance sheet calculations would really be helpful. it is easy once if you understand the simple concept. It gives you the finest values if you can do it very carefully@.

Hope the following will be helpful.

You could calculate the whole thermodynamic states of the cycle (Otto, Diesel, dual, Atkinson). To do this you will need some basic information such as the compression ratio, the cycle itself, entrance thermodynamic conditions, pressure (MAP sensor) and temperature. Each process in the cycle has its corresponding energy balance. Some approximations could be done in order to have a closed cycle, like air is always the work substance (no combustion, but heat added; no exhaust gases, but air; no air admision neither exhaust gases, but heat rejected). Taking air as the substance you still could calculate using the exact method (air properties tables) or the approximate method (Cp, Cv, k of air). Results are much better through the exact method.

Ideal gas equation is valid for both methods, so p1v1/T1 = p2v2/T2 = p3v3T3 = p4v4/T4.

The compression process is considered to be adiabatic and reversible, so r = v1/v2 = vr1/vr2 (see table A17 Cengel), and you can find T2. Heat added will depend on the cycle. If Otto then heat added is equal to delta internal energy. If Diesel then heat added is equal to delta enthalpy. In both cycles you need to stablish properly heat added in terms of kJ/kg. Expansion process (also considered adiabatic and reversible) for Otto cycle is a process in which 1/r = v3/v4 = vr3/vr4. So you will find T4. Expansion process (idem) for diesel cycle will include the cut injection ratio rc, so that rc/r = v3/v4 = vr3/vr4, and you also find T4. Finally, for Otto and Diesel engine, heat rejected is equal to delta internal energy. What you need is T4. The more trusted are your original data, the more trusted will be T4. Be very careful specially with the pressure at the admision valve and with the heat added value (which can be stablished through a combustion analysis) and good luck.

The thermodynamic two-Zone model can be used to estimate the temperature [Reference: John B. Heywood, internal combustion engine fundamentals]. Other calculation methods are presented in the same reference.