Recent measurements by Siebers et al. have shown that the flame of a high pressure Diesel spray stabilizes under quiescent conditions at a location downstream of the fuel injector. The effects of various ambient and injection parameters on the flame "lift-off" length have been investigated under typical Diesel conditions in a constant-volume combustion vessel. In the present study, the experiments of Siebers et al. have been modeled using a modified version of the KIVA-3V engine simulation code. Fuel injection and spray breakup are modeled using the KH-RT model that accounts for liquid surface instabilities due to the Kelvin-Helmholtz and Rayleigh-Taylor mechanisms. Combustion is simulated using Convergent Thinking's recently developed detailed transient chemistry solver (SAGE) that allows for any number of chemical species and reactions to be modeled. While detailed chemistry is believed to be an accurate methodology for modeling Diesel combustion, in the past the extensive run times rendered it impractical. To expedite the calculations, SAGE has been implemented into KIVA using the Message-Passing Interface (MPI). This implementation allows for the chemical reactions to be simulated in parallel on multiple CPUs. An n-heptane mechanism was used to model Diesel fuel ignition and combustion.

Multi-Dimensional Modeling of Direct-Injection Diesel Spray Liquid Length and Flame Lift-off Length using CFD and Parallel Detailed Chemistry

An apparent heat release rate (AHRR) correlation is presented for direct injection diesel engines. It is based on algebraic expressions describing the fuel burning rate as a function of dominant controlling parameters, such as ignition delay and equivalence ratio. Relating the burning rate to these parameters permits the AHRR at one engine running condition to be linked to the AHRR at another condition. By simulating the combustion process via an analytical expression whose governing parameters are linked to in-cylinder conditions, the AHRR empirical correlation simulates the combustion process (heat release) and enables the effect of many engine design and ambient condition changes to be predicted automatically, such as compressor and turbocharger match, valve and injection timing, compression ratio, aftercooling, and other engine design parameters. The correlation includes the influence of these parameters both on combustion and on the turbocharging process. While the experimental approach can reduce engine development costs, it should not replace fundamental research on diesel engine combustion nor detailed mathematical combustion modeling since it cannot predict the effect of combustion chamber design changes.

A Combustion Correlation for Diesel Engine Simulation

Available correlations for the ignition delay in pulsating, turbulent, two-phase, reacting mixtures found in a diesel engine often have limited predictive ability, especially under transient conditions. This study focuses on the development of an ignition delay correlation, based on engine data, which is suitable for predictions under both steady-state and transient conditions. Ignition delay measurements were taken on a heavy-duty diesel engine across the engine speed/load spectrum, under steady-state and transient operation. The dynamic start of injection was calculated by using a skip-fire technique to determine the dynamic needle lift pressure from a measured injection pressure profile. The dynamic start of combustion was determined from the second derivative of measured cylinder pressure. The inferred ignition delay measurements were correlated using a modified Arrhenius expression to account for variations in fuel/air composition during transients. The correlation has been compared against a number of available correlations under steady-state conditions. In addition, comparisons between measurements and predictions under transient conditions are made using the extended thermodynamic simulation framework of Assanis and Heywood. It is concluded that the proposed correlation provides better predictive capability under both steady-state and transient operation.

A Predictive Ignition Delay Correlation Under Steady-State and Transient Operation of a Direct Injection Diesel Engine

Jatropha-curcas as a non-edible methyl ester biodiesel fuel source is used to run single cylinder, variable compression ratio, and four-stroke diesel engine. Combustion characteristics as well as engine performance are measured for different biodiesel – diesel blends. It has been shown that B50 (50% of biodiesel in a mixture of biodiesel and diesel fuel) gives the highest peak pressure at 1750 rpm, while B10 gives the highest peak pressure at low speed, 1000 rpm. B50 shows upper brake torque, while B0 shows the highest volumetric efficiency. B50 shows also, the highest BSFC by about (12.5–25%) compared with diesel fuel. B10 gives the highest brake thermal efficiency. B50 to B30 show nearly the lowest CO concentration, besides CO concentration is the highest at both idle and high running speeds. Exhaust temperature and NO x are maximum for B50. Delay period is measured and correlated for different blends. Modified empirical formulae are obtained for each blend. The delay period is found to be decreased with the increase of cylinder pressure, temperature and equivalence ratio.

Experimental investigations of ignition delay period and performance of a diesel engine operated with Jatropha oil biodiesel

Multi-zone modeling of Diesel engine fuel spray development with vegetable oil, bio-diesel or Diesel fuels

An Empirical Formula for Computing the Pressure Rise Delay of a Fuel from Its Cetane Number and from the Relevant Parameters of Direct-Injection Diesel Engines

H. O. Hardenberg

Papers

An Empirical Formula for Computing the Pressure Rise Delay of a Fuel from Its Cetane Number and from the Relevant Parameters of Direct-Injection Diesel Engines