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Technical Paper

Evaluation of SOF Effects on Deposit Characteristics of the EGR Cooler Using a PM Generator

The high concentration of particulate matter (PM) in diesel exhaust gas causes significant soot deposition on the wall of EGR cooler, and reduces the heat transfer performance of the EGR cooler and the reduction rate of NOx. The deposition of PM tends to be occurred more severely with "heavy wet PM," which is more frequently at the LTC (low temperature combustion) engine. The objective of this work is to evaluate the effects of soluble organic fraction (SOF) on deposit characteristics of the EGR cooler. To measure reliable mean particle concentration values and surrogate SOFs, the soot generator with SOF vaporizer was used. As for two surrogate SOFs, n-dodecane and diesel lube oil, deposit mass increased when they were injected. Especially from the experiment results, it was found that the lube oil effect was more significant than the n-dodecane effect and lube oil also had a stronger effect on reduction of thermal conductivity by filling pores in deposits.
Technical Paper

Experimental Study on the Oxidation of Model Gases - Propylene, N-Butane, Acetylene at Ambient Temperature by Non-Thermal Plasma and Photocatalyst

Two features to facilitate chemical reactions at low temperature, non-thermal plasma and the weak dependency of photocatalyst on temperature, have been exploited by many researchers to effectively decompose hydrocarbon emissions emitted until the light-off of a three-way catalyst in spark ignition engines. To develop a realizable emissions reduction reactor, as part of such effort, this study investigates for the three model gases, propylene, n-butane and acetylene: 1) the conversion efficiency of the emissions reduction reactor, which utilizes the effect of dissociation, ionization-by-collision of the non-thermal plasma and the photocatalytic effect of TiO2, and 2) the concentrations of the products such as acetaldehyde, acetic acid, polymerized hydrocarbons and NO2. The operating parameters to obtain the plasma energy density ranging from 7.8 to 908 J/L were varied.
Technical Paper

Flame propagation measurement using ionization probes during fast acceleration

Flame propagation was detected with ionization probes located at a spark plug and a head gasket to study the relations of ionization signal to the flame propagation period. Five ionization probes were inserted at a spark plug to detect the initial flame development and eight ionization probes were inserted at a head gasket to detect the overall flame propagation. Experiments were done while the A/F ratio, load and engine speed were varied. In the fast acceleration period, lean peak phenomenon due to the fuel wall wetting occurred for one or two cycles. Ionization signals were used to determine the flame propagation duration during fast acceleration and the lean peak could be avoided by injecting proper amount of fuel.
Technical Paper

Hydrogen Effect on the DeNOX Efficiency Enhancement of Fresh and Aged Ag/Al2O3 HC-SCR in a Diesel Engine Exhaust

HC-SCR is more convenient when compared to urea-SCR, since for HC-SCR, diesel fuel can be used as the reductant which is already available onboard the vehicle. However, the DeNOX efficiency for HC-SCR is lower than that of urea-SCR in both low and high temperature windows. In an attempt to improve the DeNOX efficiency of HC-SCR, the effect of hydrogen were evaluated for the fresh and aged catalyst over 2 wt.% Ag/Al₂O₃ using a Euro-4 diesel engine. In this engine bench test, diesel fuel as the reductant was injected directly into the exhaust gas stream and the hydrogen was supplied from a hydrogen bomb. The engine was operated at 2,500 rpm and BMEP 4 bar. The engine-out NOX was around 180 ppm-200 ppm. H₂/NOX and HC₁/NOX ratios were 5, 10, 20, and 3, 6, 9, respectively. The HC-SCR inlet exhaust gas temperatures were around 215°C, 245°C, and 275°C. The catalyst volumes used in this test were 2.5L and 5L for both fresh and aged catalysts.
Technical Paper

Low Temperature Active Regeneration of Soot Using Hydrogen in a Multi-Channel Catalyzed DPF

Diesel particulate filter (DPF) systems are being used to reduce the particulate matter emissions of diesel vehicles. The DPF should be regenerated after certain driving hours or distance to eliminate soot in the filter. The most widely used method is active regeneration with oxygen at 550~650°C. Fuel penalty occurs when the exhaust gas temperature is increased. The low temperature oxidation technique is needed to reduce fuel consumption. In this study, we found that hydrogen could be used to decrease the PM oxidation temperature significantly on a catalyzed DPF (CDPF). The oxidation characteristics of PM with hydrogen supplied to CDPF were studied using a partial flow system. The partial flow system was used to control temperature and a flow rate independently. The CDPF was coated with Pt/Al₂O₃ 25g/ft₃, and a multi-channel CDPF (MC CDPF) with a square cross section of 1.65 cm width and length of 10 cm was used.
Technical Paper

Measurements and Predictions of Steady-State and Transient Stress Distributions in a Diesel Engine Cylinder Head

A combined experimental and analytical approach was followed in this work to study stress distributions and causes of failure in diesel cylinder heads under steady-state and transient operation. Experimental studies were conducted first to measure temperatures, heat fluxes and stresses under a series of steady-state operating conditions. Furthermore, by placing high temperature strain gages within the thermal penetration depth of the cylinder head, the effect of thermal shock loading under rapid transients was studied. A comparison of our steady-state and transient measurements suggests that the steady-state temperature gradients and the level of temperatures are the primary causes of thermal fatigue in cast-iron cylinder heads. Subsequently, a finite element analysis was conducted to predict the detailed steady-state temperature and stress distributions within the cylinder head. A comparison of the predicted steady-state temperatures and stresses compared well with our measurements.
Technical Paper

Spark-Ignition Engine Knock Control and Threshold Value Determination

Knock control algorithms were developed for a spark-ignition engine. Spark timing was controlled using cylinder block vibration signal. The vibration signal of a 1.5 L four cylinder spark-ignition engine was measured using an accelerometer which was attached to the cylinder block. The maximum amplitude of the bandpass-filtered accelerometer signals was used as the knock intensity. Three different spark-ignition engine knock control algorithms were tested experimentally. Two algorithms were conventional algorithms in which knock threshold values were predetermined for each engine condition. Spark timing was retarded and advanced depending on the knock intensity in one algorithm and the knock occurrence interval in the other algorithm. The third algorithm was a new algorithm in which knock threshold values were automatically corrected by monitoring knock condition.