Lurun Zhong

Split Injection Strategy for Prompt Cold Starting and Low White Smoke Emissions

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.Copyright

Effect of Nozzle hole Geometry on a HSDI Diesel Engine-Out Emissions

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). Theexperiments 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), NO x , Bosch smoke unit (BSU), CO and hydrocarbons are investigated. The results show that the 430 VCO produced longer ignition delays and cool flames of longer durations and higher intensities than its counterpart, the 320 mini sac nozzle, under all the operating conditions At zero EGR, the analysis of the data for the two nozzles showed the dependence of NO x on the premixed combustion fraction, and the dependence of smoke on the mixing controlled and diffusion controlled combustion fraction. The impact of EGR on this dependence is examined. Also, the trade-off between the engine-out emissions of NO x and Bosch Smoke Unit is determined for the two nozzles.

A mathematical model for the cranking period in the cold start of diesel engines

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.Copyright

Effect of Smoothing the Pressure Trace on the Interpretation of Experimental Data for Combustion in Diesel Engines

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. The spline function was found to be the most effective method for smoothing both the steady state pressure trace and the transient state pressure trace.

A Phenomenological Model for Combustion and Emissions in Small Bore, High Speed, Direct Injection Diesel Engines

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).Copyright