以太坊私有链-挖矿blockNumber总是为0是什么原因

现象

部署好私有链后，创建账户，执行挖矿命令 miner.start(),执行了很久发现账号余额还是0

blockNumber也是0；使用geth的默认配置blockNumber会增加很快，使用了自定义的配置

{
  "config": {
        "chainId": 15,
        "homesteadBlock": 0,
        "eip155Block": 0,
        "eip158Block": 0
    },
    "coinbase" : "0x0000000000000000000000000000000000000000",
    "difficulty" : "0x40000",
    "extraData" : "",
    "gasLimit" : "0xffffffff",
    "nonce" : "0x0000000000000042",
    "mixhash" : "0x0000000000000000000000000000000000000000000000000000000000000000",
    "parentHash" : "0x0000000000000000000000000000000000000000000000000000000000000000",
    "timestamp" : "0x00",
    "alloc": { }
}

参数的含义参考：

以太