A new instrument for measurement of diesel in-cylinder radiation heat transfer has been designed, calibrated, and tested in a single cylinder, open chamber, turbocharged diesel engine. The unique feature of the instrument is that it measures the total radiation flux over the entire hemisphere, rather than being restricted to a finite acceptance angle of less than 2π steradians as have previous instruments.The paper gives the instrument design details and shows that a combination of polycrystalline alumina and sapphire gives an optimum receiver optics design. However a solution to the problem of bonding these two materials was not found. Thus an all polycrystalline alumina receiver was used in the prototype instrument.Results using the prototype show that keeping the receiver free of soot is a problem for an all polycrystalline alumina design. Data were thus corrected for window deposits by post-experiment calibration of the dirty receiver.The effective temperature for an equivalent hemisphere was observed to be as high as 2530 K. Peak radiation flux ranged from 0.68 to 1.64 MW/m2 and increased with load. For light to medium loads, the ratio of average total radiation flux to average total flux ranged from 5 to 14%, Data are also given for cyclic variations of the total instantaneous flux to a point on the head just above the edge of the combustion bowl.