Rapid determination and detection method for automobile fuel vapor leakage

Abstract

A method for quickly judging the leakage of automobile fuel vapor is provided, which measures the volume of fuel vapor V1, determines the air pressure Pc at the starting point of the detection sampling and the air pressure Pz at the ending point, takes the absolute leakage amount Φ of the fuel vapor in a specified state within the specified detection time T as the limit value, calculates the average absolute leakage amount δ per unit time, starts sampling timing from Pc, obtains the calculated absolute leakage amount Φi at time Ti and the calculated air pressure Pi of the fuel vapor; Te is set as the starting time of the quick judgment, in the time interval from Te to T, when the fuel vapor pressure Pji detected at any time Ti is greater than or equal to Pi at the same time, it is quickly judged that the leakage is qualified and the detection is ended, or when Pji is less than Pz, it is quickly judged that the leakage is unqualified and the detection is ended, and when the quick judgment cannot be made, the detection and judgment are continued until the detection is ended at time T.

Description

Technical Field

[0001] The invention discloses a method for quickly judging the leakage of automobile fuel vapor, which is a process of quickly judging whether the leakage of fuel vapor is qualified by using the instantaneous fuel vapor pressure during the process of detecting the leakage amount within a relatively long prescribed time, and belongs to the field of automobile environmental protection detection technology. Background Art

[0002] The existing technology uses a fixed air pressure difference to quickly determine whether the fuel vapor leakage is qualified or not according to Appendix E of the national standard GB18285-2018 "Gasoline Vehicle Pollutant Emission Limits and Measurement Methods (Dual Idle Method and Simple Working Condition Method)". However, for the same technical condition of fuel vapor leakage, the larger the volume of fuel vapor, the smaller the air pressure loss. Without measuring the volume of fuel vapor, it is difficult to accurately and quickly determine whether the fuel vapor leakage is qualified or not. The absolute leakage volume within a specified time can accurately reflect the technical condition of fuel vapor leakage in the fuel tank. The volume of fuel vapor in the fuel tank of an in-use vehicle is large, and a longer leakage detection time is required to have a corresponding air pressure difference within a certain range. In order to determine a small or large leak in a shorter time, a rapid determination detection method for automobile fuel vapor leakage is used to shorten the detection time and improve the detection efficiency while ensuring accurate determination. Summary of the invention

[0003] The automobile fuel vapor leakage rapid judgment detection method is based on the absolute leakage limit and the measured fuel vapor volume of the fuel tank. According to the characteristics of fuel vapor leakage, the air pressure loss method is adopted to quickly judge whether the fuel vapor leakage is qualified by using the detection air pressure Pji and the calculation air pressure Pi at the same time. It can end the detection ahead of time if it is a very small or large leakage in a relatively short time.

[0004] Use higher-pressure gas in a container of known volume to pressurize the fuel vapor in the fuel tank. Stop pressurizing after reaching a certain pressure. Measure the air pressure P1 and temperature t1 of the fuel vapor in the fuel tank before pressurization. The volume V1 of the fuel vapor in the fuel tank is an unknown number. V1 is equal to the system volume of the fuel tank minus the volume of the fuel. Measure the air pressure P2 and temperature t2 of the fuel vapor in the fuel tank after pressurization. The volume V2 of the compressed fuel vapor after pressurization is a function of V1, P1×V1 / (273+t1)=P2×V2 / (273+t2), V2=P1×V1×(273+t2) / [P2×(273+t1)]. The gas pressure P3 and temperature t3 of the pressurized container before pressurization are measured. The gas volume V3 in the container is a known value. The gas pressure P4, temperature t4 and pressurization time ΔS in the container after pressurization are measured. The changed volume after pressurization is V4. It can be set that t3=t4=to, to is the detected ambient temperature. The state change of the gas in the container during the pressurization process is isothermal change, P3×V3=P4×V4, V4=P3×V3 / P4, and the gas volume ΔVr=V4-V3 output from the container is a known value.

[0005] According to the pressurization time ΔS and the absolute leakage limit value Ф of fuel vapor under standard state within the specified detection time T, the fuel tank leakage ΔVs during the pressurization time is estimated, ΔVs=ΔS×Ф / T, and the gas at the state of ΔVs, P1, t1 or the gas at the state of ΔVs, P1, t2 is converted to the volume ΔV4s at the state of P4, t4, ΔV4s=P1×ΔVs×(273+t4) / [P4×(273+t1)] is a known value. If ΔS is very short relative to T, ΔVs=ΔV4s=0 can be set and not calculated.

[0006] The pressure of the fuel vapor in the inflated and pressurized fuel tank increases to P2, and the volume is compressed to V2. The remaining volume ΔVc is filled by the pressurized gas ΔVr-ΔV4s output from the container, P4×(ΔVr-ΔV4s) / (273+t4)=P2×ΔVc / (273+t2), ΔVc=P4×(ΔVr-ΔV4s)×(273+t2) / [P2×(273+t4)] is a known value in the calculation, V2+ΔVc=V1, there is only one unknown number V1 in the formula, the rest are known values, V1 can be calculated, or the calculation process of V1 can be simplified by setting the gas state change to an isothermal change at ambient temperature.

[0007] After V1 is known, convert the standard state Ф into the absolute leakage volume Ф1 under the fuel vapor detection state, set the sampling end point pressure Pz at T, according to Ф×101.35 / (273+23)=Ф1×Pz / (273+t2), Ф1=Ф×101.35×(273+t2) / [Pz×(273+23)], or set Ф1=Ф without conversion, detect the sampling starting point pressure of the specified time T as Pc, calculate the Pc corresponding to the known fuel vapor volume V1, Pc×V1=Pz×(V1+Ф1), Pc=Pz×(V1+Ф1) / V1, and get the limit pressure difference ΔP=Pc-Pz, Pc and ΔP vary with different V1.

[0008] Sampling starts from Pc, and the average absolute leakage per unit time is calculated as δ=Ф1 / T. The calculated absolute leakage at time Ti is Фi=δ×Ti=Ti×Ф1 / T. According to the isothermal state change calculation, Pi×(V1+Фi)=Pc×V1, and the calculated pressure of Ti fuel vapor is Pi=Pc×V1 / (V1+Фi)=T×V1×Pc / (T×V1+Ti×Ф1). When the technical condition of fuel tank leakage is constant, the fuel vapor pressure decreases as the detection time increases, and the pressure difference between the fuel vapor pressure and the detection environment atmospheric pressure decreases. The absolute leakage per second decreases as the fuel vapor pressure decreases.

[0009] Assume that the start time of quick judgment is Te, which can be selected in the range of 0.03T to 0.3T. In order to reduce the influence of comprehensive errors such as air pressure and volume measurement, the compensation air pressure k can be set, which can be selected in the range of 0 to 500Pa. In the time interval from Te to T, when the fuel vapor pressure Pji detected at any time Ti is greater than or equal to Pi at the same time, or Pji is greater than or equal to Pi+k at the same time, it means that the actual leakage from Pc to Ti is less than or equal to the calculated absolute leakage Φi, and is also less than the limit leakage corresponding to Ti. It can be quickly judged that the leakage is qualified and the detection is ended, or when Pji is less than Pz, it can be quickly judged that the leakage is unqualified and the detection is ended. When it cannot be quickly judged, the detection is continued until the time T is ended. The start time Te of the qualified and unqualified quick judgment can be set to be different, and the judgment can be made when the conditions are met at a single time point, or when the conditions are met at several consecutive time points.

[0010] The method for quickly judging the leakage of automobile fuel vapor is a method for quickly judging whether the leakage is qualified by instantaneous fuel vapor pressure, which is characterized by: the fuel vapor volume V1, the specified detection time T, the detection sampling starting point pressure Pc and the end point pressure Pz are known, the absolute leakage amount Φ of the specified state of fuel vapor within T is used as the limit value, Φ is converted into the absolute leakage amount Φ1 of the fuel vapor detection state, or Φ1=Φ is set without conversion; the sampling timing is started from Pc, and the calculated pressure of the fuel vapor at time Ti is obtained Pi=T×V1×Pc / (T×V1+Ti×Φ1), and it is set Te is the start time of quick judgment. In the time interval from Te to T, when the fuel vapor pressure Pji detected at any time Ti is greater than or equal to Pi at the same time, or Pji is greater than or equal to Pi+k at the same time, k is the compensation pressure, then the leak is quickly judged to be qualified and the detection is ended; or when Pji is less than Pz, then the leak is quickly judged to be unqualified and the detection is ended; or the start time Te of the qualified and unqualified quick judgments is different, or the quick judgment is made only when the conditions are met at several consecutive time points, and when the quick judgment cannot be made, the detection and judgment are continued until the time T when the detection is ended. DETAILED DESCRIPTION

[0011] Taking the detection of fuel tank leakage in a gasoline passenger car as an example, the specific implementation method of the rapid judgment detection method for automobile fuel vapor leakage is explained. The detection environment atmospheric pressure Po = 100.8kPa, temperature to = 32.1℃, the fuel vapor volume V1 of the fuel tank before pressurization is unknown, temperature t1 = 35.7℃, air pressure P1 = 101.4kPa, temperature t2 = 33.8℃, air pressure P2 = 104.5kPa after pressurization; the volume of the pressurized container V3 = 100L, air pressure P3 = 108.9kPa, temperature t3 = 32.2℃ before pressurization, air pressure P4 = 108.2kPa, temperature t4 = 32.2℃ after pressurization, pressurization time ΔS =16s; the specified detection time T=120 seconds, the absolute leakage amount Ф=0.2L of fuel vapor under standard conditions (air pressure 101.35kPa, temperature 23°C) within 120 seconds is taken as the limit value, and Pz=103kPa is set with reference to the air pressure at the sampling end point of the air pressure difference limit specified in Appendix E of the national standard GB18285-2018. It is assumed that the starting time for the quick judgment of qualified and unqualified leakage is the same as Te=20 seconds, Ti=20 seconds, and the compensation air pressure k=0. If one time point meets the conditions, a quick judgment is made.

[0012] 1. Calculate the relationship between V2 and V1: V2 = P1 × V1 × (273 + t2) / [P2 × (273 + t1)] = 101.4 × V1 × (273 + 33.8) / [104.5 × (273 + 35.7)] = 0.9644 V1.

[0013] 2. Calculate the volume of pressurized gas output by the pressurized container: ΔVr = V4-V3 = P3×V3 / P4-V3 = 108.9×100 / 108.2-100 = 0.647L.

[0014] 3. Calculate the fuel vapor leakage of the fuel tank during the pressurization time: ΔVs = ΔS × Ф / T = 16 × 0.2 / 120 = 0.0267; convert ΔVs into the leakage at the output termination point of the pressurized container: ΔV4s = P1 × ΔVs × (273 + t4) / [P4 × (273 + t1)] = 101.4 × 0.0267 × (273 + 32.2) / [108.2 × (273 + 35.7)] = 0.0247; ΔVr - ΔV4s = 0.647 - 0.0247 = 0.6223 L.

[0015] 4. Convert ΔVr-ΔV4s into the filling volume in the fuel tank after the fuel vapor is pressurized: ΔVc=P4×(ΔVr-ΔV4s)×(273+t2) / [(273+t4)×P2]=108.2×0.6223×(273+33.8) / [(273+32.2)×104.5]=0.6477L.

[0016] 5. Calculate the volume of fuel vapor in the car's fuel tank: V1 = V2 + ΔVc = 0.9644V1 + 0.6477, V1 = 18.194L.

[0017] 6. Quickly determine the leak

[0018] (1) Convert Ф to the absolute leakage volume Ф1 under the fuel vapor detection state: Ф1 = Ф × 101.35 × (273 + t2) / [(273 + 23) × Pz] = 0.2 × 101.35 × (273 + 33.8) / [(273 + 23) × 103] = 0.204 L.

[0019] (2) Calculate the air pressure at the specified starting time corresponding to the known V1. Pc = Pz × (V1 + Φ1) / V1 = 103 × (18.194 + 0.204) / 18.194 = 104.155 kPa.

[0020] (3) The sampling time of the vehicle is started from Pc=104.155kPa. When Ti=20 seconds is reached, the fuel vapor Pji is measured, and the calculated air pressure at the same time is Pi=T×V1×Pc / (T×V1+Ti×Ф1)=120×18.194×104155 / (120×18.194+20×0.204)=103961Pa. When Pji≥103961Pa, the leakage is judged to be qualified and the detection is terminated; or when Pje<103000Pa, the leakage is quickly judged to be unqualified and the detection is terminated; if it cannot be judged quickly, the detection and judgment are continued until the time T is reached.

[0021] The rapid determination and detection method for automobile fuel vapor leakage has the advantages of good detection and determination accuracy and fast detection, and can greatly improve the detection efficiency of the inspection station for in-use vehicles.

Claims

1. The automobile fuel vapor leakage rapid determination detection method is a method for quickly determining whether the leakage is qualified by using the instantaneous fuel vapor pressure, and is characterized by: The fuel vapor volume V1, the specified detection time T, the detection sampling starting point pressure Pc and the end point pressure Pz are known, and the absolute leakage amount Φ of the fuel vapor in the specified state within T is taken as the limit value, and Φ is converted into the absolute leakage amount Φ1 of the fuel vapor detection state, or Φ1=Φ is set without conversion; the sampling timing starts from Pc, and the calculated pressure of the fuel vapor at time Ti is obtained as Pi=T×V1×Pc / (T×V1+Ti×Φ1), and Te is set as the starting time of rapid determination. In the time interval from Te to T, when the detected fuel vapor pressure Pji at any time Ti is greater than or equal to Pi at the same time, or Pji is greater than or equal to Pi+k at the same time, k is the compensation pressure, then the rapid determination of leakage is qualified and the detection is terminated, or when Pji is less than Pz, then the rapid determination of leakage is unqualified and the detection is terminated, or the starting time Te of qualified and unqualified rapid determination is different, or the rapid determination is made only when the conditions are met at several consecutive time points, and when the rapid determination cannot be made, the detection and determination are continued until the detection is terminated at time T.