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The disturbances in the cylinder gas pressure trace caused by combustion in internal combustion engines have an impact on the shape of the rate of heat (energy) release (RHR). It is necessary to smooth the pressure trace before carrying out the RHR calculations and making any interpretations for the combustion process. Different smoothing methods are analyzed and their features compared. Furthermore, the selection of the smoothing starting point and its effect on the smoothing quality of pressure data are described. The Fast Fourier Transform (FFT) analysis is applied to determine the frequency of the disturbances in power spectrum and obtain the optimal specified smoothing parameter (SSP). The experimental data was obtained on a single-cylinder research diesel engine, running under simulated turbocharged steady state conditions. The experiments covered a wide range of engine operating parameters such as injection pressures, injection timing, and EGR ratios.

Adiabatics, Inc. with the support of the U.S. Army Tank Automotive & Armaments Command has examined the feasibility of using Diamond Like Carbon (DLC) films and Iron Titanate (Fe2TiO5 or IT) for sliding contact surfaces in Low Heat Rejection (LHR) diesel engines. DLCs have long been a popular candidate for use in sliding contact tribo-surfaces where a perceived reduction of friction losses will result in increased engine efficiency [1]. There exists a broad range of technologies for applying DLC films. This paper examines several types of these technologies and their future application to automotive internal combustion engines. Our work focuses upon DLC use for LHR military diesel engines where operating temperatures and pressures are higher than conventional diesel engines. However, a direct transfer of this technology to automotive diesel or gasoline engines exists for these thin films.

The combustion and emission characteristics of a high speed, small-bore, direct injection, single cylinder, diesel engine are investigated using two different nozzles, a 430-VCO (0.171mm) and a 320 Mini sac (0.131mm). The experiments were conducted at conditions that represent a key point in the operation of a diesel engine in an electric hybrid vehicle (1500 rpm and light load condition). The experiments covered fuel injection pressures ranging from 400 to 1000 bar and EGR ratios ranging from 0 to 50%. The effects of nozzle hole geometry on the ignition delay (ID), apparent rate of energy release (ARER, ARHR), NOx, Bosch smoke unit (BSU), CO and hydrocarbons are investigated.

Diesel engine cold-start problems include long cranking periods, hesitation and white smoke emissions. A better understanding of these problems is essential to improve diesel engine cold-start. In this study computer simulation model is developed for the steady state and transient cold starting processes in a single-cylinder naturally aspirated direct injection diesel engine. The model is verified experimentally and utilized to determine the key parameters that affect the cranking period and combustion instability after the engine starts. The behavior of the fuel spray before and after it impinges on the combustion chamber walls was analyzed in each cycle during the cold-start operation. The analysis indicated that the accumulated fuel in combustion chamber has a major impact on engine cold starting through increasing engine compression pressure and temperature and increasing fuel vapor concentration in the combustion chamber during the ignition delay period.

Integrated control strategies for the O.P.E.R.A.S. (Optimization of injection Pressure, EGR ratio, injection Retard or Advance and Swirl ratio) are demonstrated. The strategies are based on an investigation of combustion and emissions in a small bore, high speed, direct injection diesel engine. The engine is equipped with a common rail injection system and is tested under simulated turbocharged engine conditions at two loads and speeds that represent two key operating points in a medium size HEV vehicle. A new phenomenological model is developed for the fuel distribution in the combustion chamber and the fractions that are injected prior to the development of the flame, injected in the flame or deposited on the walls. The investigation covered the effect of the different operating parameters on the fuel distribution, combustion and engine-out emissions.

The paper analyses the friction in the valve train of an internal combustion engine trying to separate the contribution of the different components to the total friction losses in the valve train. The measurements are performed on a running engine in order to avoid extraneous factors introduced by simulating rigs. The experimental engine is instrumented with strain gauge bridges on the rocker arm, the push rod and the camshaft to measure forces and moments acting on these components. Original techniques are developed to isolate and determine the friction forces between the valve stem and its guide, the friction force in the rocker arm bearing and the combined friction between cam/tappet and tappet/bore. It was found that the friction in the rocker arm bearing never reaches hydrodynamic conditions and that the friction coefficient between cam and tappet reduces with an increase in the engine speed.

In view of the new regulations for diesel engine emissions, EGR is used to reduce the NOx emissions. Diluting the charge with EGR affects the autoignition, combustion as well as the regulated and unregulated emissions of diesel engines, under different operating conditions. This paper presents the results of an investigation on the effect of EGR on the global activation energy and order of the autoignition reactions, premixed and mixing-controlled combustion fractions, the regulated (unburned hydrocarbons, NOx, CO and particulates), aldehydes, CO2 and HC speciation. The experiments were conducted on two different direct injection, four-stroke-cycle, single-cylinder diesel engines over a wide range of operating conditions and EGR ratios.

An experimental setup using rapid compression machine to provide excellent optical access to visualize simulated high-speed small-bore direct injection diesel engine combustion processes is described. Typical combustion visualization results of diesel spray combustion under different EGR, swirl, and injection pressure and nozzle conditions are presented. Different swirl intensities are achieved using an air nozzle with variable orientations and a check valve to connect the compression chamber and the combustion chamber. Different EGR ratios are achieved by pre-injection of diesel fuel prior to the main observation sequence. Clear visualization of the high-pressure fuel injection, ignition, combustion and spray/wall/swirl interactions is obtained. The injection system is a high-pressure common-rail system with either a VCO or a mini-sac nozzle. High-speed movies up to 35,000 frame-per-second are taken using a framing drum camera to record the combustion events.

Combustion instability and white smoke emissions are serious problems during cold starting of diesel engines. In this investigation, a model has been applied to predict misfiring based on an analysis of the autoignition process. The effect of injection timing on combustion instability during the cold start transient, at different ambient temperatures is investigated, both theoretically and experimentally. Maps have been developed to show the zones where misfiring would occur. The experimental work was conducted on a direct injection heavy-duty diesel engine in a cold room. The room temperature covered a range from 21 ° C to -10 ° C. The cycle-by-cycle data analysis was made and results plotted on the developed maps. The experimental results correlated fairly well with the model prediction. Based on the analysis, a new strategy for cold starting can be developed to reduce combustion instability and white smoke emissions.

High-pressure fuel injection combustion is being applied as an approach to increase the power density of diesel engines. The high-pressure injection enables higher air utilization and thus improved smoke free low air-fuel ratio combustion is obtained. It also greatly increases the injection rate and reduces combustion duration that permits timing retard for lower peak cylinder pressure and improved emissions without a loss in fuel consumption. Optimization of these injection parameters offers increased power density opportunities. The lower air-fuel ratio is also conducive to simpler air-handling and lower pressure ratio turbocharger requirements. This paper includes laboratory data demonstrating a 26 percent increase in power density by optimizing these parameters with injection pressures to 200 mPa.

The high temperature tribology issue for uncooled Low Heat Rejection (LHR) diesel engines where the cylinder liner piston ring interface exceeds temperatures of 225°C to 250°C has existed for decades. It is a problem that has persistently prohibited advances in non-watercooled LHR engine development. Though the problem is not specific to non-watercooled LHR diesel engines, it is the topic of this research study for the past two and one half years. In the late 1970s and throughout the 1980s, a tremendous amount of research had been placed upon the development of the LHR diesel engine. LHR engine finite element design and cycle simulation models had been generated. Many of these projected the cylinder liner piston ring top ring reversal (TRR) temperature to exceed 540°C[1]. In order for the LHR diesel to succeed, a tribological solution for these high TRR temperatures had to be developed.

The future of maintaining a superior mobile military ground vehicle fleet rests in high power density propulsion systems. As the U.S. Government desires to convert its powerplant base to heavy fuel operation, there arises the opportunity to incorporate new advanced materials into these heavy fuel engines. These newer materials serve the purpose of decreasing powerplant weight and develop new component designs to take advantage of improved strength and temperature capability of those materials. In addition, the military continues the effort for a non-watercooled Low Heat Rejection (LHR) diesel engine. This type of engine demands the use of ceramic and advanced ceramic composite material hardware. Furthermore, today's higher pressure fuel injection systems, coupled with reduced air/fuel ratio as a means of increasing horsepower to size and weight, will require thermal protection or change in material specification for many of the engine's components.

An experimental study was carried out to visualize the spray and combustion inside an AVL single-cylinder research diesel engine converted for optical access. The injection system was a hydraulically-amplified electronically-controlled unit injector capable of high injection pressure up to 180 MPa and injection rate shaping. The injection characteristics were carefully characterized with injection rate meter and with spray visualization in high-pressure chamber. The intake air was supplied by a compressor and heated with a 40kW electrical heater to simulate turbocharged intake condition. In addition to injection and cylinder pressure measurements, the experiment used 16-mm high-speed movie photography to directly visualize the global structures of the sprays and ignition process. The results showed that optically accessible engines provide very useful information for studying the diesel combustion conditions, which also provided a very critical test for diesel combustion models.

I The effect of Cetane Number (CN) of the fuel and the addition of cetane improvers on the cold starting and white smoke emissions of a diesel engine was investigated. Tests were conducted on a single-cylinder, four-stroke-cycle, air-cooled, direct-injection, stand-alone diesel engine in a cold room at ambient temperatures ranging from 25 °C to - 5 °C. Five fuels were used. The base fuel has a CN of 49.2. The CN of the base fuel was lowered to 38.7 and 30.8 by adding different amounts of aromatic hydrocarbons. Iso-octyl nitrate is added to the high aromatic fuels in order to increase their CN to 48.6 and 38.9 respectively. Comparisons are made between the five fuels to determine the effect of CN and the additive on cylinder peak pressure, heat release rate, cold start-ability, combustion instability, hydrocarbon emissions and solid and liquid particulates.

Thin thermal barrier ceramic coatings were applied to a standard production direct injection diesel engine. The resultant fuel economy when compared to the standard metallic engine at full load and speed (2600) was 6% better and 3.5% better at 1600 RPM. Most coated diesel engines todate have not shown significant fuel economy one way or the other. Why are the results more positive in this particular case? The reasons were late injection timing, high injection pressure with high injection rates to provide superior heat release rates with resultant lower fuel consumption. The recent introduction of the high injection pressure fuel injection system makes it possible to have these desirable heat release rates at the premixed combustion period. Of course the same injection characteristics were applied to the standard and the thin thermal barrier coating case. The thin thermal barrier coated engine displayed superior heat release rate.

A two phase, global combustion model has been developed for quiescent chamber, direct injection diesel engines. The first stage of the model is essentially a spark ignition engine flame spread model which has been adapted to account for fuel injection effects. During this stage of the combustion process, ignition and subsequent flame spread/heat release are confined to a mixing layer which has formed on the injected jet periphery during the ignition delay period. Fuel consumption rate is dictated by mixing layer dynamics, laminar flame speed, large scale turbulence intensity, and local jet penetration rate. The second stage of the model is also a time scale approach which is explicitly controlled by the global mixing rate. Fuel-air preparation occurs on a large-scale level throughout this phase of the combustion process with each mixed fuel parcel eventually burning at a characteristic time scale as dictated by the global mixing rate.

This paper deals with the analysis of heat release characteristics of an insulated turbocharged, six cylinder, DI contemporary diesel engine. The engine is fully insulated with thin thermal barrier coatings. Effect of insulation on the heat release was experimentally verified. Tests were carried over a range of engine speeds at 100%, 93%, 75% and 50% of rated torque. Fuel injection system was instrumented to obtain injection pressure characteristics. The study shows that rate of heat release, particularly in the major portion of the combustion, is higher for the insulated engine. Improvement in heat release and performance are primarily attributed to reduction in heat transfer loss due to the thin thermal barrier coating. Injection pressure at the rated speed and torque was found to be 138 MPa and there was no degradation of combustion process in the insulated engine. Improvements in BSFC at 93% load are 3.25% and 6% at 1600 and 2600 RPM, respectively.

Experimental results focused towards developing tribological surface coatings coupled with liquid lubricant boundary layer effects, for advanced high temperature military diesel engine applications are presented. The primary focus of this work is in the area of advanced, low heat rejection (LHR) high output diesel engines, where high temperature boundary lubrication between the piston ring and the cylinder liner wall surface is critical for successful engine operation. The target temperature focused upon in our research is an operating top ring reversal (TRR) temperature of approximately 538°C. The technology advancement used for this application involves treating porous iron oxide/titanium oxide (Fe2O3/TiO2) and molybdenum (Mo) based composite thermal sprayed coatings with chemical binders to improve coating strength, integrity, and tribological properties. This process dramatically decreases open porosity to form an almost monolithic appearing coating at the surface1.

More stringent regulations have been enforced over the past few years on diesel exhaust emissions. White smoke emission, a characteristic of diesel engines during cold starting, needs to be controlled in order to meet these regulations. This study investigates the sources and constituents of white smoke. The effects of fuel properties, design and operating parameters on the formation and emissions of white smoke are discussed. A new technique is developed to measure the real time gaseous hydrocarbons (HC) as well as the solid and liquid particulates. Experiments were conducted on a single cylinder direct injection diesel engine in a cold room. The gaseous HC emissions are measured using a high frequency response flame ionization detector. The liquid and solid particulates are collected on a paper filter placed upstream of the sampling line of the FID and their masses are determined.

The methodology for predicting the transient mixing rate is presented for a direct injection, quiescent chamber diesel. The mixing process is modeled as a zero-dimensional, large-scale phenomena which accounts for injection rate, cylinder geometry, and engine operating condition. As a demonstration, two different injection schemes were investigated for engine speeds of 1600, 2100, and 2600 rpm. In the first case, the air-fuel ratio was fixed while the injection rate was allowed to vary, but for the second case, the injection duration was fixed and the air-fuel ratio was allowed to vary. For the former case, the resulting mixing rate was also compared with the experimentally determined fuel burning rate. These two quantities appeared to be correlated in some manner for the various engine speeds under investigation.