This paper investigates the effect of air inlet temperature on the auto-ignition of fuels that have different CN and volatility in a single cylinder diesel engine. The inlet air temperature is varied over a range of 30°C to 110°C. The fuels used are ultra-low-sulfur-diesel (ULSD), JP-8 (two blends with CN 44.1 & 31) and F-T SPK. Detailed analysis is made of the rate of heat release during the ignition delay period, to determine the effect of fuel volatility and CN on the auto-ignition process. A STAR-CD CFD model is applied to simulate the spray behavior and gain more insight into the processes that immediately follow the fuel injection including evaporation, start of exothermic reactions and the early stages of combustion. The mole fractions of different species are determined during the ignition delay period and their contribution in the auto-ignition process is examined. Arrhenius plots are developed to calculate the global activation energy for the auto-ignition reactions of these fuels. Correlations are developed for the ID and the mean air temperature and pressure.

An investigation was conducted on a 0.42 liter single cylinder diesel engine equipped with a common rail fuel injection system to evaluate the influence of the swirl motion on JP-8 fuel combustion. Engine tests were performed under steady state conditions of 5 bar IMEP and 1500 RPM. Two different swirl ratios of 1.44 and 7.12 were applied at injection pressures ranging from 400 to 1200 bar. The apparent rate of heat release (ARHR) curve is analyzed to determine the effect of swirl on combustible mixture formation, auto-ignition, premixed and diffusion controlled combustion fractions. An attempt is made to correlate between the swirl ratio and different combustion and emissions parameters at different injection pressures. The emissions included the gaseous fractions and particulates. Two types of particulate matter were measured: Accumulation mode particles (AMPs) and Nucleation mode particles (NMPs). The results indicate that ignition delay duration of JP-8 increases as the swirl ratio increases influencing the overall combustion process and engine out emissions.

Advanced electronically controlled diesel engines require a feedback signal to the ECU to adjust different operating parameters and meet demands for power, better fuel economy and low emissions. Different types of in-cylinder combustion sensors are being considered to produce this signal. This paper presents results of an experimental investigation on the characteristics of the ion current in an automotive diesel engine equipped with a common rail injection system. The engine is a 1.9 L, 4-cylinder, direct injection diesel engine. Experiments covered different engine loads and injection pressures. The relationships between the ion current, combustion parameters and engine out NO emissions and opacity are presented. The analysis of the experimental data identified possible sources of the ion current produced in diesel engines.

Concern about the depletion of petroleum reserves, rising prices of conventional fuels, security of supply and global warming have driven research toward the development of renewable fuels for use in diesel engines. These fuels have different physical and chemical properties that affect the diesel combustion process. This paper compares between the autoignition, combustion, performance and emissions of soybean derived biodiesel, JP-8 and ultra low sulfur diesel (ULSD) in a high speed single-cylinder research diesel engine equipped with a common rail injection system. Tests were conducted at steady state conditions at different injection pressures ranging from 600 bar to 1200 bar. The ‘rate of heat release’ traces are analyzed to determine the effect of fuel properties on the ignition delay, premixed combustion fraction and mixing and diffusion controlled combustion fractions. Biodiesel produced the largest diffusion controlled combustion fraction at all injection pressures compared to ULSD and JP-8. At 600 bar injection pressure, the diffusion controlled combustion fraction for biodiesel was 53% whereas both JP-8 and ULSD produced 39%. In addition, the effect of fuel properties on engine performance, fuel economy, and engine-out emissions is determined. On an average JP-8 produced 3% higher thermal efficiency than ULSD. Special attention is given to the NOx emissions and particulate matter characteristics. On an average biodiesel produced 37% less NOx emissions compared to ULSD and JP-8.

Biodiesel has different physical and chemical properties than ultra low sulfur diesel fuel (ULSD). The low volatility of biodiesel is expected to affect the physical processes, mainly fuel evaporation and combustible mixture formation. The higher cetane number of biodiesel is expected to affect the rates of the chemical reactions. The combination of these two fuel properties has an impact on the auto ignition process, subsequently combustion and engine out emissions. Applying different swirl ratios and injection pressures affect both the physical and chemical processes. The focus of this paper is to investigate the effect of varying the swirl ratio and injection pressure in a single-cylinder research diesel engine using a blend of biodiesel and ULSD fuel. The engine is a High Speed Direct Injection (HSDI) equipped with a common rail injection system, EGR system and a swirl control mechanism. The engine is operated under simulated turbocharged conditions with 3 bar Indicated Mean Effective Pressure (IMEP) at 1500 rpm, using 100% ULSD and a blend of 20% biodiesel and 80% ULSD fuel. The biodiesel is developed from soy bean oil. A detailed analysis of the apparent rate of heat release (ARHR) is made to determine the role of the biodiesel component of B-20 in the combustible mixture formation, autoignition process, premixed, mixing controlled and diffusion controlled combustion fractions. The results explain the factors that cause an increase or a drop in NO x emissions reported in the literature when using biodiesel.

The cam-tappet contact experiences very high loads and the lubrication conditions are Elasto-Hydrodynamic (EHD). In EHD lubrication the oil film thickness (OFT) is mainly determined by the entrainment speed of the oil and the oil viscosity. Under the high load present in the cam-tappet contact the OFT reaches very small values in the order of magnitude of a fraction of one micrometer and asperity contacts cannot be avoided. In this situation the friction force has two components, a boundary and a viscous one, and non-Newtonian behavior of the oil prevails. The friction force is determined by the rheological properties of the oil and the geometry of the contact (combined radius of curvature, cam width and combined asperity of the rubbing surfaces). For valve trains with bucket type tappets, the mechanism is design to rotate the tappet during engine operation. In this situation, both the entrainment speed and the radius of curvature are varying along the contact line determining variations in the OFT and, consequently, variations in the contribution of the boundary friction component. Based on a simulation model that considers the tappet spin under the action of the friction force between cam and tappet, and the friction force between tappet and its bore, the entrainment speeds and their directions were calculated along the contact line. It was found that the boundary friction component reaches a maximum value at the inner edge of the cam, at the beginning of the valve-closing event. Because the boundary component of the friction force is mainly responsible for wear, an increased wear of this region should occur. Visual inspection of a used camshaft seems to confirm this finding.

Advance high speed direct injection diesel engines apply high injection pressures, exhaust gas recirculation (EGR), injection timing and swirl ratios to control the combustion process in order to meet the strict emission standards. All these parameters affect, in different ways, the ignition delay (ID) which has an impact on premixed, mixing controlled and diffusion controlled combustion fractions and the resulting engine-out emissions. In this study, the authors derive a new correlation to predict the ID under the different operating conditions in advanced diesel engines. The model results are validated by experimental data in a single-cylinder, direct injection diesel engine equipped with a common rail injection system at different speeds, loads, EGR ratios and swirl ratios. Also, the model is used to predict the performance of two other diesel engines under cold starting conditions.

Adiabatics INC. with the support of U.S. Army Tank Automotive and Armaments Command has developed a new high temperature lubricant with additives package to work under the rigid regime of advanced Low Heat Rejection (LHR) diesel engine operating parameters. Using the newly developed high temperature lubricant on a laboratory tribology test bench and on a single cylinder LHR engine, the Army specified requirements of 410 °C Top Ring Reversal (TRR), 175 °C sump temperatures, and friction coefficient of 0.085–0.10 have been met. We have used the test data generated from the laboratory tribology test bench, and the LHR single cylinder test engine to validate the eight tribology performance parameters. The eight tribology parameters are: Oil Film thickness, shear stress, shear rate, temperature, effective viscosity, wear, specific friction work, and contact stress. Also this paper includes test data for the newly designed lubricating and cooling system. Further testing will be conducted on a multi cylinder production engine to complete the validation process of the newly developed lubricant and the lubricating and cooling system.

This paper reports the development and formulation of a new cost effective means of applying ceramic tribology coatings to sealing rings. This coating, though developed with the support of the U.S. Army Tank Automotive and Armaments Command for use on Low Heat Rejection (LHR) high output diesel engines, can be used on any internal engine compression seal ring. It is not limited for use in LHR diesel engines. Applying ceramic coating, especially on the compression piston ring, reduces the friction losses and wear of sliding contact surfaces. This will result in increased engine efficiency and durability. The work presented examines both laboratory and small bore engine testing of this technology. Laboratory tribometer tests compare the ceramic coating to existing and experimental piston ring tribosurfaces. Friction and wear performance demonstrated in the laboratory is verified for use in LHR diesel engine application. Low raw material cost coupled with ease of application and high deposit efficiency of the ceramic make this coating a viable candidate for commercialization.

This paper introduces a phenomenological model for the fuel distribution, combustion, and emissions formation in the small bore, high speed direct injection diesel engine. A differentiation is made between the conditions in large bore and small bore diesel engines, particularly regarding the fuel impingement on the walls and the swirl and squish gas flow components. The model considers the fuel injected prior to the development of the flame, fuel injected in the flame, fuel deposited on the walls and the last part of the fuel delivered at the end of the injection process. The model is based on experimental results obtained in a single-cylinder, 4-valve, direct-injection, four-stroke-cycle, water-cooled, diesel engine equipped with a common rail fuel injection system. The engine is supercharged with heated shop air, and the exhaust back pressure is adjusted to simulate actual turbo-charged diesel engine conditions. The experiments covered a wide range of injection pressures, EGR rates, injection timings and swirl ratios. Correlations and 2-D maps are developed to show the effect of combinations of the above parameters on engine out emissions. Emphasis is made on the nitric oxide and soot measured in Bosch Smoke Units (BSU).

The paper presents a generic model of a turbocharged, common rail diesel engine developed on a SIMULINK platform. The model is developed for the main task of predicting transient behavior of the turbocharged engine, especially acceleration under load. In order to reduce computer time, the model is zero-dimensional as far as combustion is concerned, but split injection is considered to simulate the main characteristic of modern common rail diesel engines. A simplified generic model of the turbocharger is developed such as to determine the effects of different design parameters on the acceleration of the engine. A detailed dynamic model of the engine is considered to allow estimating the torsional behavior of the crankshaft and evaluate the impact of torsional vibrations. The model is validated on a four-cylinder, 2.5 liter common-rail diesel engine and is further used to identify the fueling strategy and the design parameters that could be improved in order to obtain the best possible engine acceleration under different load conditions.

The low temperature combustion regime (LTC) has been known to simultaneously reduce both NOx and smoke emissions. The concept is to burn the fuel vapor-air charge, low in oxygen concentration, at low temperatures to reduce the formation of both NO x and smoke emissions. The paper investigates two combustion concepts in the LTC regime, the MK (modulated kinetics) and the smokeless locally rich diesel combustion and proposes a new strategy for a further reduction in emissions with minimum penalty in fuel economy. Tests were carried out under simulated turbo charged conditions on a single cylinder, small bore HSDI diesel engine with a re-entrant bowl combustion chamber. The engine is equipped with a common rail fuel injection system. Tests covered a wide range of injection pressures, EGR rates, injection timings and swirl ratios to determine their individual and collective contributions in engine-out emissions and fuel economy within this combustion regime. The proposed strategy is based on the results of this experimental investigation.

Progressing needs for prompt cold start of direct injection Diesel engines is the motivation behind this study. Authors have examined the autoignition and combustion processes in the early firing cycles of the engine and proposed a strategy to reduce the cranking period and the white smoke emissions. The concept is to accelerate the preparation of the combustible mixture during the cranking process. This is achieved by splitting the injected fuel in two parts and controlling its timing. The duration of the first injection is limited such that the spray penetrates through the combustion chamber and evaporates before it reaches the walls. The dwell between the two injections is adjusted to allow time for the first spray to mix with the fresh charge, form a combustible mixture and start producing the autoignition radicals. The second part would evaporate and autoignite by reacting with the radicals before it reaches the cool walls. The strategy is verified on a 1.2 L Ford Diata Diesel engine equipped with a first generation common rail fuel injection system. The cycle resolved hydrocarbons, and NOx emissions are measured by high response detectors. In addition, the mass and constituents of the white smoke are measured. All the experiments for this paper have been conducted after the engine has been soaked at the normal room temperature for at least eight hours. The results showed that there is an optimum strategy for the split injection that would minimize the cranking period and white smoke emissions.

In a single cylinder engine, the speed fluctuation during steady state operation of the engine is influenced only by the cylinder pressure variation, the engine friction and the dynamics of the crankshaft. This dependency is used to explore the capacity of the lumped mass model of the crankshaft to correctly represent its dynamics. Based on this model, the paper establishes the relationship between the cylinder pressure variation and the crankshaft speed fluctuation for steady state operation of the single cylinder diesel engine. Correlations are determined between the harmonic components of the tangential gas-pressure and the harmonic components of the angular speed of the free end of the crankshaft. These correlations are used to predict the angular speed variation of the crankshaft, when the cylinder pressure variation is known, or to reconstruct the cylinder pressure when the crankshaft speed fluctuation is known. The reverse calculation of the pressure variation from the measured crankshaft speed is strongly influenced by the elastic characteristics of the crankshaft. If the stiffness of the crankshaft is not accurately determined, the results are significantly distorted.

This paper presents tribological modeling and experimental work of tribology parameters of a fired single cylinder turbocharged diesel engine run at various loads, speeds, intake boost pressures, and cylinder liner temperatures. Analysis were made on piston rings-liner materials, rings mechanical and thermal loads, contact pressure between rings-liner, and lubricant conditions. In order to validate the engine tribology models the engine tribology parameters were measured, the tribology parameters are oil film thickness and coefficient of friction between rings-liner, friction force, friction power; shear rate, shear stress and wear of the sliding surfaces. The measurement of oil film thickness was accomplished on instrumented single cylinder AVL turbocharged diesel engine using the difference in voltage drop method between ring-liner. The oil film thickness was measured for all three piston rings, the compression ring, the second ring, and the oil ring.

A mathematical model is developed to predict the length of the cranking period of direct injection diesel engines at low ambient temperatures. The model takes into consideration the physical and chemical process that develop in the cylinder over the whole cranking period. The model accounts for the variation in the following: (a) fuel accumulated in the cylinder in both the liquid and the vapor phases, (b) gas temperature and pressure, (c) wall temperature and (d) the autoignition reactions rate. An “Autoignition Index” (AI) is developed to account for the combined effects of fuel volatility and its Cetane Number. The model considers that autoignition starts in the cycle where AI reaches a critical value at the end of the cranking period. The model predictions are compared with the experimental data obtained on a single cylinder diesel engine tested in a cold room using four distillate fuels having different volatilities and Cetane numbers.

The engine cooling system for a typical class 3 pickup truck with a medium duty diesel engine was modeled with a commercial code, GT-Cool in order to explore the benefit of controllable electric pump on the cooling performance and the fuel economy. As the first step, the cooling system model with a conventional mechanical coolant pump was validated with experimental data. After the model validation, the mechanical pump sub-model was replaced with the electric pump submodel and then the potential benefit of the electric pump on fuel economy was investigated with the simulation. Based on coolant flow analysis the modified thermostat hysteresis was proposed to reduce the recirculating flow and electric pump effort, thus enabling assessment of the full power saving potential. It was also demonstrated that the radiator size could be reduced without any cooling performance penalty by replacing mechanical pump with the electric pump and decoupling of the pump speed from engine speed. The predicted results indicate that the cooling system with the electric pump can dramatically reduce the pump power consumption during the FTP 74 driving schedule and that radiator can be down-sized by more than 27% of the original size under grade load condition.