Seiichi Shiga

A study of the combustion and emission characteristics of compressed-natural-gas direct-injection stratified combustion using a rapid-compression-machine

The objective of the present study is to determine the characteristics of combustion and emissions of compressed-natural-gas (CNG) direct-injection combustion using a rapid-compression-machine which has a compression ratio of 10 and a disc-shaped combustion chamber. Combustion and emission characteristics are compared for three types of fuel injection (single side, parallel side and opposed side injection) and a homogeneous mixture. The results show that with fuel injection, the fuel could be burned up to an equivalence ratio φ of 0.2 with sufficiently high combustion efficiency except for the case of φ = 1.0, while with a homogeneous mixture, the lean burn limit was only φ = 0.6 with poor combustion producing higher unburned CH4 By adjusting the location of the spark plug and fuel injectors, the combustion limit was extended to φ = 0.02. The Combustion efficiency of the injection modes is over 0.95 except for φ = 1.0 and φ < 0.06 which gave a lower combustion efficiency. Incomplete combustion in the stratified rich zone reduced the combustion efficiency at large values of φ, and possible occurrence of bulk quenching resulted in the lower combustion efficiency for very lean mixtures. Combustion efficiency for the homogeneous mixture decreases greatly with leaner mixtures, which is probably due to the thicker quenching layer near the wall. Combustion duration with fuel injection was insensitive to φ and was much shorter than for the homogeneous mixture. It was also shown that the number and location of the injectors and the injection rate had little influence on the combustion and the exhaust emissions including NOx. The pressure rise due to combustion in the case of fuel injection is higher compared to that of homogeneous mixture combustion due to the lower heat loss to the combustion chamber walls resulting from a short combustion duration. Thus it is shown that stratified-combustion with extremely lean burn capability can be realized with CNG direct injection.

Performance and emission characteristics of a diesel engine fueled with coconut oil–diesel fuel blend

Abstract The objective of the present study is to reveal the effects of pure coconut oil and coconut oil–diesel fuel blends on the performance and emissions of a direct injection diesel engine. Operation of the test engine with pure coconut oil and coconut oil–diesel fuel blends for a wide range of engine load conditions was shown to be successful even without engine modifications. It was also shown that increasing the amount of coconut oil in the coconut oil–diesel fuel blend resulted in lower smoke and NO x emissions. However, this resulted in an increase in the BSFC. This was attributed to the lower heating value of neat coconut oil fuel compared to diesel fuel.

The effect of coconut oil and diesel fuel blends on diesel engine performance and exhaust emissions

The effect of a coconut oil as diesel fuel alternatives or as direct fuel blends are investigated using a single-cylinder, direct-injection diesel engine. The spray characteristics in terms of the mean droplet diameter of these fuels were measured with a phase Doppler Anemometer. Operation of the test engine with the pure coconut oil and coconut oil–diesel fuel blends for a wide range of engine operating conditions was shown to be successful even without any engine modification. Results show that neat coconut oil fuels gave lower smoke and NOx emissions.

Effect of Fuel Injection Timing Relative to Ignition Timing on the Natural-Gas Direct-Injection Combustion

The effect of fuel injection timing relative to ignition timing on natural gas direct-injection combustion was studied by using a rapid compression machine (RCM). The ignition timing was fixed at 80 ms after the compression start. When the injection timing was relatively early (injection start at 60 ms), the heat release pattern showed a slower burn in the initial stage and a faster burn in the late stage, which is similar to that of flame propagation of a premixed gas. In contrast to this, when the injection timing was relatively late (injection start at 75 ms), the heat release rate showed a faster burn in the initial stage and a slower burn in the late stage, which is similar to that of diesel combustion. The shortest duration was realised at the injection end timing of 80 ms (the same timing as the ignition timing) over a wide range of equivalence ratio. The degree of charge stratification and the intensity of turbulence generated by the fuel jet are considered to cause this behavior. Early injection leads to longer duration of the initial combustion, whereas late injection leads to a longer duration of the late combustion. Early injection showed relatively lower CO concentration in the combustion products while late injection gave relatively lower NO x . It was suggested that early injection leads to combustion with weaker stratification, and late injection leads to combustion with stronger stratification. Combustion efficiency was kept at a high value over a wider range of equivalence ratio.

Combustion characteristics of natural-gas direct-injection combustion under various fuel injection timings

Abstract The characteristics of natural-gas direct-injection combustion under various fuel injection timings were studied by using a rapid compression machine. Results show that natural-gas direct injection can result in combustion that is much faster than homogeneous combustion while shortening the time interval between injection timing and ignition timing can markedly decrease the combustion duration. Unburned hydrocarbon would increase over a wide range of equivalence ratios, shortening the time interval between injection timing and ignition timing can decrease the value to that of homogeneous-mixture combustion. The NOx level is high but the CO level is low over a wide range of equivalence ratios and is little affected by fuel injection timing. High values of pressure rise due to combustion can be realized and it is insensitive to the variation in fuel injection timing. High combustion efficiency can be achieved, which is also independent of injection timing.

Study of cycle-by-cycle variations of natural gas direct injection combustion using a rapid compression machine

Abstract Cycle-by-cycle variations of natural gas direct injection (CNG DI) combustion were studied by using a rapid compression machine. Results show that CNG DI combustion can realize high combustion stability with less cycle-by-cycle variation in the maximum pressure rise, the maximum rate of pressure rise and the maximum rate of heat release at the given equivalence ratios. Mixture stratification and fast flame propagation with the aid of turbulence produced by the high speed fuel jet are considered to be responsible for these behaviours. Cycle-by-cycle variations in combustion durations and combustion products present higher magnitudes than those of maximum pressure rise and maximum rate of heat release. Cycle-by-cycle variations of CO and unburned CH4 show an interdependence with the variation of the late combustion duration, and the variation of NO x shows an interdependence with the variation of the rapid combustion duration. Cycle-by-cycle variations are found to be insensitive to the equivalence ratios in CNG DI combustion.

Correlation of Ignitability with Injection Timing for Direct Injection Combustion Fuelled with Compressed Natural Gas and Gasoline

Abstract A study on the correlation of ignitability with fuel injection timing for direct injection combustion fuelled with natural gas and gasoline was carried out by using a rapid compression machine. The injection pressure of natural gas is 9 MPa and the injection pressure of gasoline is 7 MPa. The study results show that natural gas direct injection possesses higher momentum than that of gasoline, and this is beneficial to the combustion enhancement since a higher intensity of turbulence could be induced. Correlation of ignitability with injection timing shows better behaviour in natural gas direct injection, and this correlation is insensitive to injection modes in the case of natural gas. Thus, natural gas direct injection would have better engine applicability under cold-start conditions. The lean burn limits of natural gas and gasoline direct injection can extend to extremely low equivalence ratio when the ignitable stratified mixture exists around the spark electrode gap by optimizing the injection timing.

Visualization study of natural gas direct injection combustion

Abstract A visualization study of natural gas direct injection combustion was carried out by using a high speed video camera. The results show that the distribution of the stratified mixture di ers with the injection mode, with parallel and single injection tending to form a higher degree of mixture stratification than opposed injection. Flame propagates toward the downstream direction in the cases of parallel and single-injection combustion, and flame propagates outward from the centre of the combustion chamber in the case of opposed injection combustion. A characteristic of turbulent combustion with a wrinkled flame front is presented in natural gas direct injection combustion. Super-lean combustion can be realized owing to the formation of an ignitable stratified mixture with the optimum setting of the fuel injection timing.

Effect of exhaust gas recirculation on diesel knock intensity and its mechanism

Abstract This paper presents an experimental study of the effect of exhaust gas recirculation (EGR) on diesel knock intensity, which is defined and discussed. In a previous paper, it was reported that particulate emission can be decreased by applying EGR under certain operating conditions; and the possible mechanism of the effect of EGR was presented. In the present study, the effect of EGR on diesel knock is examined under a variety of operating conditions. Diesel knock intensity is decreased considerably by EGR under the same operating conditions as when the particulate emission is decreased. A quantitative relationship between the diesel knock intensity and the maximum rate of cylinder pressure rise is obtained. The effect of EGR on diesel knock intensity is determined by both the chemical reaction rate of the initial premixed combustion (spontaneous ignition) and the fuel mass fraction prepared and burned in this stage. This is verified by measuring the ignition lag and classifying it into chemical and physical lags by a statistical technique presented by S. Kumagai.

Thrust Measurement of a Rectangular Hypersonic Nozzle Using an Inclined Baffle Plate

Thrust measurement of a rectangular hypersonic nozzle employed in the precooled turbojet engine under development in the JapanAerospace Exploration Agency is carried out using an inclined baffle plate. A 1.0%-scaled model of the nozzle was manufactured, and its gross thrust was investigated. The hypersonic nozzle has a variable throat and an external ramp to compensate the drastic change in the nozzle pressure ratio through the operation. At takeoff, an intensive jet noise is expected due to the high-speed exhaust jet, and in the present study, the impact of aerodynamic-tab jet noise suppressors on the thrust vector of the nozzle is investigated. Because of the simplicity, a baffle plate, which basically provides an on-axis forcemeasurement, is applied to a simultaneousmeasurement of the magnitude andangle of the thrust vector by giving anangle to the impact surface relative to the jet. It is shown that the magnitude of the thrust vector is kept constant regardless of the aerodynamic-tabmass fraction, which implies that a lossless mixing between the main jet and aerodynamic tab can be assumed. It is also shown that the thrust angle changes with the increase in the aerodynamic-tab mass fraction because of the deformation of the jet cross section.