Search Results

A thermodynamic analysis of mixture formation in cylinders that takes into account mixture inhomogeneity and the wall film is presented. Conditions for obtaining low hydrocarbon emission are clarified analytically as a function of the fuel mass of the wall film and inhomogeneity of the mixture. Optimum processes for atomizing and vaporizing fuel are presented to reduce the inhomogeneity and the fuel mass of the film.

The usage of Compressed Natural Gas (CNG) engines is increasing as requirements for cleaner emissions are required by state and federal agencies such as C.A.R.B. and E.P.A. Also, to further reduce emission levels, tighter air/fuel ratio control is required. There are many ways to control air/fuel ratio on a CNG engine. It can be performed in a feedforward method, a feedback method or a combination of both. CNG fuel can be introduced to the engine via single-point injection, multi-point injection or with an air/gas mixer. Mixer-type and single-point injection are good candidates for the application of a gas flow sensor for accurate air/fuel ratio measurement. Reduction of valve hysteresis can also be achieved. Fuel delivery and control systems cost can be kept low compared to using multi-point injection where high flow injectors are required for each cylinder. A gas flow sensor is placed in the CNG stream to monitor mass gas flow rate.

Emissions tests were performed to study the operating characteristics of a wide range air/fuel ratio (AFR) sensor in closed loop control. The AFR sensor used here has an output voltage with respect to AFR that is linear and can be characterized by a fourth order polynomial function. For this study the output signal of the AFR sensor was fed into a General Control Unit (GCU). The GCU converted this analog input signal into a square wave similar to a lambda sensor. The output from the GCU was fed into the Engine Control Unit (ECU) of the 3.8L, V6 test engine to control the engine A/F ratio. Emissions tests were conducted in closed loop mode under steady state and transient condition. Emissions of HC, CO and NOx using the AFR sensor will be shown. Results of these tests showed that the AFR sensor allowed for precise control of the AFR at the stoichiometric point (λ = 1.0).

To detect an air-fuel ratio in wide range is very important to control the automotive engines with low fuel consumption and low exhaust emissions. Although the application of zirconia electrolyte for this purpose has been proposed by the authors several years ago, there remained several problems due to the contamination of gas diffusion apertures which are exposed to the exhaust gas environment. Here the behavior of ions transported in zirconia electrolyte have been analyzed to optimize the structure and characteristics, and to guarantee the long life operation of sensor. Gas contents and their reactions in combustion process under the wide range air-fuel ratio have been analyzed, and these results were reflected to the analysis of ion transportation in zirconia electrolyte. Experimental results supported the analytical results, and they showed the possibilities of long life operation of zirconia air-fuel ratio sensor utilizing ion transportation phenomena.

Engine performance has been investigated of currently gasoline powered passenger car engines converted to methanol and gasoline mixtures. A 4 cycle, 4 cylinder, 1.6 liter displacement engine for a conventional passenger car was tested varying the fueling condition. The mixing ratio of methanol to gasoline was changed from zero percent to one hundred percent, discreetly. Evaluation of engine performance was made to find the optimum air-fuel ratio and spark timing in each mixed fuel condition. It has been clarified that the stoichiometric air-fuel ratio in the mixed fuel can be determined by the mixing ratio P, as an expression of The MBT(minimum spark advance for the best torque) characteristics for each mixed fuel codition show that the large retardation of spark timing will be required for the higher mixture ratio fuels. Changes in characteristics of fuel supply and air-fuel ratio sensing devices were investigated experimentally.

Effects of mixture formation of fuel injection systems on gasoline engine performance have been studied. Several fuel injectors which produced various spray diameters and spray patterns were used in engine tests. Spray behavior in an air flow was investigated to clarify the spray distribution through the intake valve. The relationships between the spray distribution near the intake valve and the HC emission or engine response were considered. The amount of HC emissions increased if fuel was injected when the intake valve was open with a heavy load (e.g. an engine speed of 2000 rpm and a manifold pressure of 98 kPa), because fuel would flow into the cylinders one-sidedly, causing a liquid film to form. The amount of HC emissions also increased if fuel was injected when the intake valve was open with a light load (e.g. during idling), because the fuel injection pulse would be short and fuel would flow into the cylinders, but the air-fuel mixing would not be enough to cause a misfire.

A new air-fuel ratio control algorithm and its effect on automotive engine operation is described. The system consists of a wide range air-fuel ratio sensor and a single point injector with an ultrasonic fuel atomizer. The air-fuel ratio control adopts PID control and it has built-in learning control. A 16 bit microcomputer is used for the latter. The results of three studies are given. The first deals with adaptive PID gain control for various conditions. The second is the new learning control which uses an integration terra. The third is individual cylinder air-fuel ratio control.

Mixture formation technology for gasoline engine multipoint fuel injection systems has been investigated. The fuel injector's spray, the volatility of droplets floating in the air flow, the movement of droplets around the intake valve's upper surface, the volatility of droplets on heated surfaces, and the process of atomizing droplets in the intake valve air flow was analyzed. Droplet diameters and spray patterns for good mixture formation without liquid film in cylinders have been clarified. When sequential injection is used for better responsiveness in fuel injection systems, engine performance may be reduced through increased HC emissions in some conditions. Reducing the diameter of spray droplets and preventing fuel from concentrating in the intake valve promotes vaporization, reduces fuel concentration on cylinder walls, and prevents reductions in engine performance.