Figure 10. Pressure gradient magnitude contours. ( a ) 137 μs; ( b ) 155 μs; ( c ) 160 μs; ( d ) 230 μs. Regions surrounded by black Figure 10. Pressure gradient magnitude contours. ( a ) 137 µ s; ( b ) 155 µ s; ( c ) 160 µ s; ( d ) 230 µ s. Regions surrounded by black lines represent fresh gas regions. lines represent fresh gas